Support syncing assets for other repos

As mentioned in [actions-sync issue 43](https://github.com/actions/actions-sync/issues/43), we need a tool to sync not only actions git repos but also assets (release binaries) from github.com to Github Enterprise Servers. This is especially true for repos like [actions/node-versions](https://github.com/actions/node-versions). Adding the capability for mirroring node-versions and other frequently-referenced assets would be instrumental in reducing traffic to github.com and also avoid rate limits for users of Github Enterprise Server.