Feature request: Install with restore from rdb.

[greenaar]

Fresh install works perfectly.

We have a use case where we'd use KeyDB instead of redis, but we need to do install-with-restore (in our case from an rdb file stored in a bucket).

While it's reasonable to assume that the mechanism for getting the RDB from s3 might be too large an ask, it would be nice to have:

1. Fetch an rdb (ie wget by default) - this could be a url or a passthrough to a shell script perhaps, to allow for someone writing their own handler to get the file down to disk.
2. restore the rdb as part of initial bootup
3. mark the restore as done so a helm upgrade doesn't retry it.

If it's an unreasonable request, please let me know, and we will evaluate the effort required to fork and apply this ourselves.

Thanks!