Add documentation or better error messaging for GCP OIDC error

[bender2352]

Describe the feature

Sometimes users get the following error when using GCP OIDC: The size of mapped attribute exceeds the 127 bytes limit.

There's nothing we can do here because this is a size limit imposed by GCP: https://github.com/google-github-actions/auth/blob/main/docs/TROUBLESHOOTING.md#subject-exceeds-the-127-byte-limit

Add documentation and/or a better error message for the user.

Why is this feature important?

No response

Additional context

No response