Validate Cognitive Search Code Generation in CI

[alzimmermsft]

Description

Adds an Update-Codegeneration.ps1 script into the Swagger folder for azure-search-documents which will cause CI to validate that code generation is up-to-date for the SDK.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[benbp]

Suggested change

	& (Join-Path $PSScriptRoot ".." ".." ".." ".." eng scripts Invoke-Codegeneration.ps1) -Directory $PSScriptRoot -AutorestOptions '--tag=package-2021-04-30-Preview-searchindex'
	& (Join-Path $PSScriptRoot ".." ".." ".." ".." eng scripts Invoke-Codegeneration.ps1) -Directory $PSScriptRoot -AutorestOptions '--tag=package-2021-04-30-Preview-searchservice'
	$gitRoot = git rev-parse --show-toplevel
	& (Join-Path $PSScriptRoot $gitRoot eng scripts Invoke-Codegeneration.ps1) -Directory $PSScriptRoot -AutorestOptions '--tag=package-2021-04-30-Preview-searchindex'
	& (Join-Path $PSScriptRoot $gitRoot eng scripts Invoke-Codegeneration.ps1) -Directory $PSScriptRoot -AutorestOptions '--tag=package-2021-04-30-Preview-searchservice'

[alzimmermsft]

I'm going to save this change for a later date, mainly due to the need to know what git rev-parse --show-toplevel does compared to direct path hierarchy traversal (..)