docs: add missing AWS_IAM to auth_provider in appsync_api

[auvred]

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

Description

AWS_IAM is a valid auth provider type.

I copied the order of possible values from here for better consistency:

terraform-provider-aws/website/docs/r/appsync_api.html.markdown

Lines 164 to 168 in d74e0fd

	### Auth Modes
	The `connection_auth_mode`, `default_publish_auth_mode`, and `default_subscribe_auth_mode` blocks support the following:
	* `auth_type` - (Required) Type of authentication. Valid values: `API_KEY`, `AWS_IAM`, `AMAZON_COGNITO_USER_POOLS`, `OPENID_CONNECT`, `AWS_LAMBDA`.

References

https://docs.aws.amazon.com/appsync/latest/APIReference/API_AuthProvider.html#appsync-Type-AuthProvider-authType

[github-actions]

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[jar-b]

LGTM 🚀

[jar-b]

Thank you for the correction, @auvred! 🔍

[github-actions]

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[github-actions]

This functionality has been released in v6.13.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!