This adds various new locks to replace the single big lock on
the head. All parts now must be COW as they may be held by clients
after initial retrieval.
Series by ID and hashes are now held in a stripe lock to reduce
contention and total holding time during GC. This should reduce
starvation of readers.
Implement labels.PrefixMatcher and use interface conversion in querier
to optimize label tuples search.
[unit-tests]: Fix bug and populate label index for mock index.
Signed-off-by: Dmitry Ilyevsky <ilyevsky@gmail.com>
Fabian Reinartz
Dmitry Ilyevsky
Julius Volz
Goutham Veeramachaneni