Support storage and restore of cache from an external server

[twodrops]

We have a self-hosted GitHub Enterprise which does not support actions/cache. maxnowack/local-cache worked out-of-the-box and indeed it is a real drop-in replacement for actions/cache :)

We need to support self-hosted and ephemeral runners. For ephemeral runners, I was thinking of uploading/rsycing the created tarball to a central data store and restoring from there. In that end, it would make this action like actions/cache, but with the difference that it is not tied to GitHub Infrastructure and the storage can be configured.

Could you please assess the complexity of implementing the use case? I'm looking for guidance on the best starting point within the codebase to begin this work and contribute. Any suggestions or insights would be greatly appreciated.