Improve postcommit execution

Todays a thread that commit a transaction has an afterCompletion to fire a PostCommitEventExecutor in charge of running a thread to do postcommit stuff.

The result is that the main thread wait with a timeout of 300ms a reply from the postcommit thread, in case of timeout we have the warning:

Events postcommit execution exceeded timeout of 300ms, leaving thread running

This kind of execution is expected in some case where a thread execute multiple transaction and assume that the postcommit listeners are completed before the next transaction.

But there are other use case where we don't mind if the postcommit is treated as async and it is unnecessary to wait for a reply before continuing.

In this case we should have a flag (or whatever mechanism) to say that we should not wait for postcommit return.