ci: ingest gitlab docs in production environment

Note: This is a high priority MR for Solution implementation for "users can ask docu... (gitlab-org/gitlab#451215 - closed) in %17.0

This MR is on top of ci: ingest gitlab docs in pipeline schedules (!774 - merged)

What does this merge request do and why?

This MR adds ingest:prod job to ingest/refresh gitlab-docs in production environment, which is based on ci: ingest gitlab docs in pipeline schedules (!774 - merged).

Workload Identify Federation/Provider was already setup by following the setup doc.

The variables INGEST_GCP_PROJECT_NAME, INGEST_WORKLOAD_IDENTITY_PROVIDER, and INGEST_SERVICE_ACCOUNT are switched per environment with the environment scope.

Related to Add tests for ingestion scripts (#448 - closed)

How to set up and validate locally

N/A

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.