Merge branch '508709_move_to_bounded_context' into 'master'

Move GraphQL mutations for branches into Bounded Context

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/175831



Merged-by: Vasilii Iakliushin <viakliushin@gitlab.com>
Approved-by: Fred Reinink <freinink@gitlab.com>
Approved-by: Hunter Stewart <hustewart@gitlab.com>
Reviewed-by: Vasilii Iakliushin <viakliushin@gitlab.com>
Reviewed-by: Fred Reinink <freinink@gitlab.com>
Reviewed-by: GitLab Duo <gitlab-duo@gitlab.com>