Merge branch 'axil-update-built-in-project-templates-development-docs' into 'master'

Update built-in project templates development docs

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/126248



Merged-by: Evan Read <eread@gitlab.com>
Approved-by: Javiera Tapia <jtapia@gitlab.com>
Approved-by: Janis Altherr <jaltherr@gitlab.com>
Approved-by: Evan Read <eread@gitlab.com>
Reviewed-by: Achilleas Pipinellis <axil@gitlab.com>
Reviewed-by: Javiera Tapia <jtapia@gitlab.com>
Co-authored-by: Achilleas Pipinellis <axil@gitlab.com>