add iam_tags to vault_aws_secret_backend_role

[thyton]

Description

This PR adds iam_tags to vault_aws_secret_backend_role resource, picking up the remaining work on #2087

Closes #1073

Checklist

• Added CHANGELOG entry (only for user-facing changes)
• Acceptance tests where run against all supported Vault Versions

Output from acceptance testing:

~/go/src/github.com/hashicorp/terraform-provider-vault (add-iam-tags-to-aws-secret-backend) $ make testacc TESTARGS='-run=TestAccAWSSecretBackendRole'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test -run=TestAccAWSSecretBackendRole -timeout 30m ./...
?   	github.com/hashicorp/terraform-provider-vault	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/cmd/coverage	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/cmd/generate	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/helper	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/internal/consts	[no test files]
ok  	github.com/hashicorp/terraform-provider-vault/codegen	0.402s [no tests to run]
?   	github.com/hashicorp/terraform-provider-vault/internal/identity/group	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/internal/identity/mfa	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/internal/pki	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/internal/sync	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/schema	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/util/mountutil	[no test files]
ok  	github.com/hashicorp/terraform-provider-vault/internal/identity/entity	0.584s [no tests to run]
ok  	github.com/hashicorp/terraform-provider-vault/internal/provider	0.814s [no tests to run]
ok  	github.com/hashicorp/terraform-provider-vault/testutil	1.059s [no tests to run]
ok  	github.com/hashicorp/terraform-provider-vault/util	1.256s [no tests to run]
ok  	github.com/hashicorp/terraform-provider-vault/vault	0.766s

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[fairclothjm]

LGTM

[vinay-gopalan]

LGTM! Tests and TF scripts work as expected. Thanks for adding support for this :)

[thyton]

Thank you!