Update metadata because Gitaly group has moved from Create to Systems

doc/administration/gitaly/configure_gitaly.md

doc/administration/gitaly/index.md

doc/administration/gitaly/monitoring.md

doc/administration/gitaly/praefect.md

doc/administration/gitaly/recovery.md

doc/administration/gitaly/reference.md

doc/administration/gitaly/troubleshooting.md

doc/administration/operations/moving_repositories.md

doc/administration/raketasks/praefect.md

doc/administration/repository_checks.md

doc/administration/repository_storage_paths.md

doc/administration/repository_storage_types.md

doc/administration/server_hooks.md

doc/api/project_repository_storage_moves.md

doc/development/git_object_deduplication.md

doc/development/gitaly.md

doc/user/admin_area/settings/gitaly_timeouts.md

...er/project/repository/reducing_the_repo_size_using_git.md