Validate IAM role names

### TL;DR

It's common to introduce a typo when listing an IAM role in the `google_project_iam_member` resource.

Guardian could use the [IAM roles list API](https://cloud.google.com/sdk/gcloud/reference/iam/roles/list) to retrieve all of the roles from the project that is going to be modified and validate the string before merging a change.

### Detailed design

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### Alternatives considered

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### Additional information

_No response_

Find where google_project_iam_member resources are processed. Use the Google Cloud IAM roles list API to fetch valid roles for the target project. Add validation to compare the provided role name against the retrieved list. Look for existing API client usage and error handling patterns in the codebase.

Written by the indexing model from the issue text.