[Support v4] Fix unqueue first then publish

[jokesterfr]

We wait for the publisher to fully push the events before flushing the queue. If concurrent .commit() calls are performed this could lead to IDEMPOTENT WRITE errors on the eventstore side, leading to unsent events.

This PR aims at flushing the events before sending them to the publisher, drastically reducing error probability.

[jokesterfr]

Could this be merged to a v4 support branch?

[jokesterfr]

IMO a good implementation would commit events without any manual commit() call, just setting rules about refresh frequency and/or events count per batch.

On the implementation side this would be a simple setInterval() calling the publishers on a regular basis if uncommitted events remain.

[jokesterfr]

We also should deprecate the auto commit feature sooner or later.