Request to add ts.add latest sample event

[vzambo64]

Time-series module emits "ts.add:dest" event when the latest bucket is closed and a new bucket is opened in a destination rule compacted time-series.
No event is emitted if data is received and compacted to the latest bucket until the bucket is closed, so this event has a latency at least of the bucket time after the time-series latest value is changed.
The LATEST flag allows to include the actual value of the latest bucket in the requesting commands. When the task is to process the actual value of a destination rule time-series there is no event to listen for the latest bucket changes.
Suggesting to add a ts.add:dest:latest event by inserting the following lines into the module.c as the last statement in the handleCompaction function:
RedisModule_NotifyKeyspaceEvent( ctx, REDISMODULE_NOTIFY_MODULE,"ts.add:dest:latest", rule->destKey);
This is emitting the event message when a sample is added from a source as the highest timestamp sample into the destination time-series. The subscriber receiving the event can get and process the latest value of the time-series.
If the event notification results in a significant performance drop a configuration argument might be added to conditionally turn on this event notification.
(I have a branch for it in a fork...)