This allows querying two PathInfoService implementations sequentially,
and inserts into the "near" one if it's not there yet.
There is no negative cache, and put / listing is not implemented (for
now).
Change-Id: I24c3d0e0c3c2f0524a6cc7b2f3cbc33eb20cf92b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11636
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>