Auto sync to new repos

This is a "nice to have" feature. When a new repo is created, the file syncer should detect and sync to it. This also goes for repos that are deleted, they should not be synced to and not require a PR for this change. In other words, this should be automated and not require manual intervention for which repos should be synced to or syncing should not be attempted on non-existent/deleted repos.

Start by locating the file syncer entry point in the repository and read how it discovers repositories and decides whether to create a PR. Define the behavior for newly created, deleted, and non-existent repositories, then verify that syncing requires no manual repository list changes and deleted repositories do not trigger PRs.

Written by the indexing model from the issue text.