Feature: Codegen and support for transform endpoints

[tyrannosaurus-becks]

This PR adds support for a nascent code generation functionality. The intent of code generation is to speed up the development process, and to provide more standardized (and hopefully less buggy) code. As it's used for more resources and data sources, templates and logic will likely need to be tweaked to accommodate them. The codegen package includes a README.md describing how to use it properly.

This PR also adds support for the following generated endpoints:

• "/auth/jwt/config" as a resource Update from @catsby 2020-07-01: This duplicated the existing resource_jwt_auth and was removed in remove the jwt/config resource from the code generated files #807
• "/transform/alphabet/{name}" as a resource
• "/transform/decode/{role_name}" as a data source
• "/transform/encode/{role_name}" as a data source
• "/transform/role/{name}" as a resource
• "/transform/template/{name}" as a resource
• "/transform/transformation/{name}" as a resource

Since this is a large PR, it's likely there will be a large number of comments/changes on the code. For those, please either 1) PR or commit them directly into this feature branch to add them to the present PR, or 2) close this PR, add more to the branch, and re-PR.

Thank you!

Related test output

=== RUN   TestCodeFilePath
--- PASS: TestCodeFilePath (0.00s)
=== RUN   TestDocFilePath
--- PASS: TestDocFilePath (0.00s)
=== RUN   TestStripCurlyBraces
=== RUN   TestStripCurlyBraces/{test}
=== RUN   TestStripCurlyBraces/{{name}}
=== RUN   TestStripCurlyBraces/name
=== RUN   TestStripCurlyBraces/{name
--- PASS: TestStripCurlyBraces (0.00s)
    --- PASS: TestStripCurlyBraces/{test} (0.00s)
    --- PASS: TestStripCurlyBraces/{{name}} (0.00s)
    --- PASS: TestStripCurlyBraces/name (0.00s)
    --- PASS: TestStripCurlyBraces/{name (0.00s)
=== RUN   TestFormat
=== RUN   TestFormat/alphabet
=== RUN   TestFormat/{name}
=== RUN   TestFormat/{role_name}
=== RUN   TestFormat/{name}#01
=== RUN   TestFormat/{version}
=== RUN   TestFormat/unlikely
=== RUN   TestFormat/{role_name_}
=== RUN   TestFormat/{role__name}
=== RUN   TestFormat/{role_name_here}
=== RUN   TestFormat/{rOlE_nAmE}
=== RUN   TestFormat/{ROLE_NAME}
--- PASS: TestFormat (0.00s)
    --- PASS: TestFormat/alphabet (0.00s)
    --- PASS: TestFormat/{name} (0.00s)
    --- PASS: TestFormat/{role_name} (0.00s)
    --- PASS: TestFormat/{name}#01 (0.00s)
    --- PASS: TestFormat/{version} (0.00s)
    --- PASS: TestFormat/unlikely (0.00s)
    --- PASS: TestFormat/{role_name_} (0.00s)
    --- PASS: TestFormat/{role__name} (0.00s)
    --- PASS: TestFormat/{role_name_here} (0.00s)
    --- PASS: TestFormat/{rOlE_nAmE} (0.00s)
    --- PASS: TestFormat/{ROLE_NAME} (0.00s)
=== RUN   TestValidate
=== RUN   TestValidate/nil_inputs_error
=== RUN   TestValidate/blank_endpoints_error
=== RUN   TestValidate/blank_dirnames_error
=== RUN   TestValidate/blank_upper_case_differentiators_error
=== RUN   TestValidate/blank_lower_case_differentiators_error
=== RUN   TestValidate/valid_endpoint
=== RUN   TestValidate/bad_parameter_type
=== RUN   TestValidate/good_parameter_type
=== RUN   TestValidate/array_of_strings_param
=== RUN   TestValidate/array_of_objects_param
--- PASS: TestValidate (0.00s)
    --- PASS: TestValidate/nil_inputs_error (0.00s)
    --- PASS: TestValidate/blank_endpoints_error (0.00s)
    --- PASS: TestValidate/blank_dirnames_error (0.00s)
    --- PASS: TestValidate/blank_upper_case_differentiators_error (0.00s)
    --- PASS: TestValidate/blank_lower_case_differentiators_error (0.00s)
    --- PASS: TestValidate/valid_endpoint (0.00s)
    --- PASS: TestValidate/bad_parameter_type (0.00s)
    --- PASS: TestValidate/good_parameter_type (0.00s)
    --- PASS: TestValidate/array_of_strings_param (0.00s)
    --- PASS: TestValidate/array_of_objects_param (0.00s)
=== RUN   TestToTemplatableParam
--- PASS: TestToTemplatableParam (0.00s)
=== RUN   TestParseParameters
=== RUN   TestParseParameters//transform/role/{name}
=== RUN   TestParseParameters//transform/alphabet/{name}
--- PASS: TestParseParameters (0.00s)
    --- PASS: TestParseParameters//transform/role/{name} (0.00s)
    --- PASS: TestParseParameters//transform/alphabet/{name} (0.00s)
=== RUN   TestTemplateHandler
--- PASS: TestTemplateHandler (0.00s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/codegen	(cached)
?   	github.com/terraform-providers/terraform-provider-vault/generated	[no test files]
=== RUN   TestDecodeBasic
--- PASS: TestDecodeBasic (0.26s)
=== RUN   TestDecodeBatch
--- PASS: TestDecodeBatch (0.30s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/generated/datasources/transform/decode	0.580s
=== RUN   TestEncodeBasic
--- PASS: TestEncodeBasic (0.27s)
=== RUN   TestEncodeBatch
--- PASS: TestEncodeBatch (0.30s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/generated/datasources/transform/encode	0.594s
=== RUN   TestConfig
--- PASS: TestConfig (0.79s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/generated/resources/auth/jwt	0.813s
=== RUN   TestAlphabetName
--- PASS: TestAlphabetName (0.59s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/generated/resources/transform/alphabet	0.608s
=== RUN   TestRoleName
--- PASS: TestRoleName (0.59s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/generated/resources/transform/role	0.614s
=== RUN   TestTemplateName
--- PASS: TestTemplateName (0.48s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/generated/resources/transform/template	0.690s
=== RUN   TestTransformationName
--- PASS: TestTransformationName (0.38s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/generated/resources/transform/transformation	0.396s
=== RUN   TestParsePath
=== RUN   TestParsePath/my/transform/hello
=== RUN   TestParsePath/jwt-1914071788362821795
=== RUN   TestParsePath/accounting-transit
--- PASS: TestParsePath (0.00s)
    --- PASS: TestParsePath/my/transform/hello (0.00s)
    --- PASS: TestParsePath/jwt-1914071788362821795 (0.00s)
    --- PASS: TestParsePath/accounting-transit (0.00s)
=== RUN   TestPathParameters
=== RUN   TestPathParameters//transform/role/{name}
=== RUN   TestPathParameters//transit/sign/{name}/{urlalgorithm}
=== RUN   TestPathParameters//transit/sign/{name}/{urlalgorithm}#01
=== RUN   TestPathParameters//auth/approle/tidy/secret-id
=== RUN   TestPathParameters//sys/mfa/method/totp/{name}/admin-generate
--- PASS: TestPathParameters (0.00s)
    --- PASS: TestPathParameters//transform/role/{name} (0.00s)
    --- PASS: TestPathParameters//transit/sign/{name}/{urlalgorithm} (0.00s)
    --- PASS: TestPathParameters//transit/sign/{name}/{urlalgorithm}#01 (0.00s)
    --- PASS: TestPathParameters//auth/approle/tidy/secret-id (0.00s)
    --- PASS: TestPathParameters//sys/mfa/method/totp/{name}/admin-generate (0.00s)
PASS
ok  	github.com/terraform-providers/terraform-provider-vault/util	0.008s

[catsby]

Merging this in, thanks @tyrannosaurus-becks !