Merge branch 'jv-gitaly-pack-objects-feature-flag' into 'master'

Add Gitaly feature flag definition

See merge request gitlab-org/gitlab!68879

config/feature_flags/development/gitaly_pack_objects_hook_with_sidechannel.yml

+---
+name: gitaly_pack_objects_hook_with_sidechannel
+introduced_by_url: https://gitlab.com/gitlab-org/gitaly/-/merge_requests/3758
+rollout_issue_url: https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/1187
+milestone: '14.3'
+type: development
+group: 'team::Scalability'
+default_enabled: false