Feature: GCE for Alerting

When the data source is configured with Forward OAuth Identity, queries authenticate by forwarding the signed-in user's OAuth token to BigQuery. Alert rules evaluate in the background with no user session, so there is no token to forward and the query reaches BigQuery with no credentials:

googleapi: Error 401: Request is missing required authentication credential.
Expected OAuth 2 access token... reason: CREDENTIALS_MISSING

This makes alerting unusable on instances that rely on OAuth identity forwarding.

The solution is to give the users the ability to use a different authentication mechanism for alerts in case they need it or just keep it same as the main authentication.

I've made a PR already for my proposed solution, which is already tested and Fully backward compatible.

https://github.com/grafana/google-bigquery-datasource/pull/532

@zoltanbedi

Start by reviewing linked pull request #532, which contains the proposed and tested solution. Check how alert-rule queries authenticate when Forward OAuth Identity is enabled, and verify that alerts can use a separate mechanism or retain the main authentication while remaining backward compatible.

Written by the indexing model from the issue text.