Merge branch '432346-validate-default-stage-name' into 'master'

Validate default VSA stage name

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/144707



Merged-by: Adam Hegyi <ahegyi@gitlab.com>
Approved-by: charlie ablett <cablett@gitlab.com>
Approved-by: Felipe Artur <fcardozo@gitlab.com>
Reviewed-by: charlie ablett <cablett@gitlab.com>