Data source: use aws_subnets over aws_subnet_ids

[rhoboat]

Description

Addresses internal aws v4 compatibility.

This updates example code only. The provider version handles both old and new data sources, so users have no updates to make on their end as a result of this change. It is backward compatible. When we bump the provider version to at least 3.75 and/or remove the 4.x lock, that's when we have a potential backward incompatibility, but most likely, even that update will be functionally backward compatible, i.e., only require an update to the provider version, and no config changes, imports, or state migrations.

Documentation

N/A

TODOs

• Ensure the branch is named correctly with the issue number. e.g: feature/new-vpc-endpoints-955 or bug/missing-count-param-434.
• Update the docs.
• Keep the changes backwards compatible where possible.
• Run the pre-commit checks successfully.
• Run the relevant tests successfully.
• Ensure any 3rd party code adheres with our license policy: https://www.notion.so/gruntwork/Gruntwork-licenses-and-open-source-usage-policy-f7dece1f780341c7b69c1763f22b1378
• Maintainers Only. If necessary, release a new version of this repo.
• Maintainers Only. If there were backwards incompatible changes, include a migration guide in the release notes.
• Maintainers Only. Add to the next version of the monthly newsletter (see https://www.notion.so/gruntwork/Monthly-Newsletter-9198cbe7f8914d4abce23dca7b435f43).

Related Issues

Addresses https://github.com/gruntwork-io/cloud-chasers/issues/20

[yorinasub17]

LGTM assuming the tests pass!

[rhoboat]

Test failures:

1. This is not related to the AWS provider, so unrelated failure.

    --- FAIL: TestValidateAllTerraformModulesOnTerratest/home/circleci/project/examples/azure/terraform-azure-frontdoor-example (3.06s)

2. Failed on fetching the syslog for the instances after the redeploy. I verified the test installs 4.12.1 of the AWS provider. Since it was able to deploy and validate the redeploy, I don't think this has to do with the code changes, like data.aws_subnets fetches failing.

=== CONT  TestTerraformRedeployExample
    ec2-syslog.go:81: 'Fetching syslog for Instance i-0ff7bf658328561de in us-west-1' unsuccessful after 120 retries

3. This ran in eu-north-1. This page verifies that t2.micro is supported in Stockholm. The AWS docs list the possible reasons for this error.
   In any case, no files were changed that would affect this test.

=== CONT  TestGetInstanceIdsForAsg
    asg_test.go:82: 
        	Error Trace:	asg_test.go:82
        	            				asg_test.go:53
        	            				asg_test.go:43
        	Error:      	Received unexpected error:
        	            	Unsupported: The requested configuration is currently not supported. Please check the documentation for supported configurations.
        	            		status code: 400, request id: f6ffd647-52b3-4559-ab82-50a086088713
        	Test:       	TestGetInstanceIdsForAsg
=== CONT  TestGetInstanceIdsForAsg
    asg_test.go:154: 
        	Error Trace:	asg_test.go:154
        	            				asg_test.go:133
        	            				panic.go:642
        	            				testing.go:756
        	            				asg_test.go:82
        	            				asg_test.go:53
        	            				asg_test.go:43
        	Error:      	Received unexpected error:
        	            	ValidationError: AutoScalingGroup name not found - null
        	            		status code: 400, request id: de4e3814-36e7-48af-b33c-710a30001db6
        	Test:       	TestGetInstanceIdsForAsg
--- FAIL: TestGetInstanceIdsForAsg (2.82s)

5. No files were changed that would affect this test. However, looking through the test, it might be flaky, so I changed it to make sure the test takes at least 25 seconds (greater than or equal to 25).

    assertion_compare.go:313: 
        	Error Trace:	apply_test.go:185
        	Error:      	"25" is not greater than "25"
        	Test:       	TestParallelism
        	Messages:   	[]
--- FAIL: TestParallelism (31.75s)

[rhoboat]

1 and 2 are still failing, but unrelated to this change.
3 and 4 have stopped failing.
Thanks for the review! Merging.