Snapshot metadata

This isnt for merging yet, just WIP,

Bit of a slow start, but figured while I am still finding my way around the codebase i'll raise this so ppl can peek at the progress more conveniently and give me feedback as i go.
> Is there a better/cleaner way to do this?

    repo.store.utf.read(...)

To just read the string, or

   jsonLines.mkString("")

But do you mean something else entirely?