Extend decomposition prometheus metric with information about CI
This adds to ci_dedicated_primary_connection="true"
to gitlab_database_decomposition_gitlab_schemas_used
to indicate whether the given schemas are evaluated in context
of a Phase 4 rollout.
This allows us to monitor whether partial Phase 4 rollout properly assigns connections to schemas.
Related to: gitlab-com/gl-infra/production#6440 (closed)
Edited by Kamil Trzciński (Back 2025-01-01)