Sync auto deploy and master branches across remotes

What does this MR do?

Add a security sync service

Creates a Security::SyncRemotesService that uses sync_branches method to sync master and auto-deploy branches after a security release is finished.

• sync_branches was moved to a module so it can be shared across ReleaseTools::Services::SyncRemotes and ReleaseToolsServices::Security::SyncRemotes
• A new rake task on security namespace was added to trigger this new service
• SyncRemotesService was also refactored a bit:
  • Security remote flag was removed
  • Comments were re-organized
  • Specs were simplified

Related to https://gitlab.com/gitlab-org/release-tools/-/issues/365