Add metadata to some unattributed feature flags

Per https://gitlab.com/gitlab-org/gitlab/-/issues/251080

config/feature_flags/development/cleanup_lfs_during_gc.yml

 ---
 name: cleanup_lfs_during_gc
-introduced_by_url: 
-rollout_issue_url: 
-group: 
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38813
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/238605
+group: group::source code
 type: development
 default_enabled: false

config/feature_flags/development/paginated_notes.yml

 ---
 name: paginated_notes
-introduced_by_url: 
-rollout_issue_url: 
-group: 
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/34628
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/254987
+group: group::source code
 type: development
 default_enabled: false

config/feature_flags/development/repack_after_shard_migration.yml

 ---
 name: repack_after_shard_migration
-introduced_by_url: 
-rollout_issue_url: 
-group: 
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/21502
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/195597
+group: group::source code
 type: development
 default_enabled: false