data-source/aws_iam_policy_document: Add version argument

[bflad]

Closes #744

Changes proposed in this pull request:

• Supports creating 2008-10-17 version IAM policy documents as the structure is the same as 2012-10-17

Output from acceptance testing:

$ make testacc TEST=./aws TESTARGS='-run=TestAccAWSDataSourceIAMPolicyDocument'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -run=TestAccAWSDataSourceIAMPolicyDocument -timeout 120m
=== RUN   TestAccAWSDataSourceIAMPolicyDocument_basic
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_basic (9.57s)
=== RUN   TestAccAWSDataSourceIAMPolicyDocument_source
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_source (12.37s)
=== RUN   TestAccAWSDataSourceIAMPolicyDocument_sourceConflicting
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_sourceConflicting (9.17s)
=== RUN   TestAccAWSDataSourceIAMPolicyDocument_override
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_override (7.61s)
=== RUN   TestAccAWSDataSourceIAMPolicyDocument_Version_20081017
--- PASS: TestAccAWSDataSourceIAMPolicyDocument_Version_20081017 (7.89s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	47.194s

[apparentlymart]

If this version is selected then AWS won't accept interpolated variables, so perhaps we should then produce an error if the user attempts to use our custom &{...} variable syntax with that version number selected... otherwise we'll replace the &{...} with ${...} but then that new form will just be interpreted literally.

[hikerspath]

Would still want to keep the lack of a version to provide the 'latest' for people that want to ensure they are already on the latest version, just looking to ensure that if people want to either lock-in or need to utilize an older version are able to do so. Thanks!

[bflad]

Replaced by #6699

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!