Merge branch '372432-centralize-onboarding-code-around-the-onboarding-namespace-wkr' into 'master'

[worker] Centralize onboarding code around the onboarding namespace

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/97526



Merged-by: Tetiana Chupryna <tchupryna@gitlab.com>
Approved-by: Smriti Garg <sgarg@gitlab.com>
Approved-by: Tetiana Chupryna <tchupryna@gitlab.com>
Co-authored-by: Doug Stull <dstull@gitlab.com>