tell-based - reconnect on leader change

tell-based - reconnect on leader change

The ShardManager is the aggregation point for shards so we need
to propagate shard leader change events etc to the ClientActorBehavior
to initiate a refresh of the backend info. The ModuleShardBackendResolver
sends a new message, RegisterForShardAvailabilityChanges, to the
ShardManager actor with a Consumer callback that is notified by the
ShardManager when events affecting shard leader availability occur.
The ModuleShardBackendResolver then propagates the event notification
to callbacks registered via a new notifyWhenBackendInfoIsStale method
exposed via the BackendInfoResolver interface, which the
ClientActorBehavior calls.

JIRA: CONTROLLER-1873
Change-Id: I9dbcabf5a75b195c811a22dd522115d329e5dc4b
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>