Now that CRDS supports incremental snapshot hashes,
SnapshotPackagerService needs to push 'em!
This commit does two main things:
1. SnapshotPackagerService now knows about incremental snapshot hashes,
and will push SnapshotPackage::IncrementalSnapshot hashes to CRDS.
2. At startup, when loading from a full + incremental snapshot, the
hashes need to be passed all the way to SnapshotPackagerService so it
can push these starting hashes to CRDS. Those values have been piped
through.
Fixes#20441 and #20423
Brooks Prumo