Merge branch '346563_refactor_fork_service' into 'master'

Refactor ForkService class

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/140575



Merged-by: Rémy Coutable <remy@rymai.me>
Approved-by: Sarah Yasonik <syasonik@gitlab.com>
Approved-by: Rémy Coutable <remy@rymai.me>
Reviewed-by: Rémy Coutable <remy@rymai.me>
Reviewed-by: Vasilii Iakliushin <viakliushin@gitlab.com>
Reviewed-by: Sarah Yasonik <syasonik@gitlab.com>
Co-authored-by: Vasilii Iakliushin <viakliushin@gitlab.com>