add a new RPC repair_colocated_tablets which is similar to the RPC
tablet_repair, but instead of repairing a single tablet it takes a set
of co-located tablets, repairs them and returns a shared repair_time
result.
This is useful because the way co-located tablets are represented
doesn't allow to repair tablets independently but only as a group
operation, and the repair_time which is stored in the tablet map is
shared with the entire co-location group.
But when repairing a group of co-located tablets we may require a
different behavior, especially considering that co-located tablets are
derived tablets of a special type. For example, we may want to skip
running repair on CDC tablets when repairing the base table.
The new RPC and the storage service function repair_colocated_tablets
allow the flexibility to implement different strategies when repairing
co-located groups.
Currently the implementation is simply to repair each tablet and return
the minimum repair_time as the shared repair time.