Merge branch 'add_pull_mirror_branch_prefix_ff_info' into 'master'

Add information about pull_mirror_branch_prefix FF

See merge request gitlab-org/gitlab!43530

ee/config/feature_flags/development/pull_mirror_branch_prefix.yml

 ---
 name: pull_mirror_branch_prefix
-introduced_by_url: 
-rollout_issue_url: 
-group: 
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/17368
+rollout_issue_url:
+group: group::source code
 type: development
 default_enabled: false