In addition to the specific permissions that are already mentioned, the project also needs the `iam.googleapis.com` API enabled, otherwise authenticating will fail with an error similar to:
```
Error authenticating: Error making API request.
URL: PUT https://localhost:8200/v1/auth/gcp/login
Code: 400. Errors:
* could not find service account key or Google Oauth cert with given 'kid' id
```
* Consistently use "Google Cloud" where appropriate
* Update GCP docs
This updates the GCP docs to use the new updated fields that will be
present in the next release of the plugin as well as fixes up some
inconsistencies between the GCP docs and other auth method
documentation.
This removes all references I could find to:
- credential provider
- authentication backend
- authentication provider
- auth provider
- auth backend
in favor of the unified:
- auth method
