Integrate Gitolite with new syncer

Created by: tsenart

• Integrate Gitolite with new syncer
  • Implement GitoliteSource and enable new syncer for Gitolite external services (#3489)
  • Implement enabled state deprecation migration of Gitolite external services
    • Migrate all disabled repos to gitolite.blacklist list.
    • Deprecate gitolite.initialRepositoryEnablement setting.
  • Update UI to remove enabled state for Gitolite repos.
  • Update UI to remove explicit deletion for Gitolite repos.

Follow up on #2025 (closed) Part of #3467 (closed)