Merge branch 'runner-issue-37487-gcp-secrets' into 'master'

Document fully-qualified secret naming for GCP secrets

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/152192



Merged-by: Marcel Amirault <mamirault@gitlab.com>
Approved-by: Romuald Atchadé <ratchade@gitlab.com>
Approved-by: Marcel Amirault <mamirault@gitlab.com>
Reviewed-by: Rich Wareham <rich.gitlab@richwareham.com>
Reviewed-by: Marcel Amirault <mamirault@gitlab.com>
Co-authored-by: Rich Wareham <rich.gitlab@richwareham.com>
Co-authored-by: Rich Wareham <rjw57@cam.ac.uk>