Transaction attempts histogram works incorrectly

[nvamelichev]

If there are any retries at all, StdTxManager will vastly overestimate the number of transaction attempts, because it observes all attempt counts, and not only the final attempt count of the transaction (either on its success or its failure)

[nvamelichev]

Mostly fixed in 2.8.1.

Note that an exception in a deferredFinally block set by Tx.deferredFinally() will not be properly reported in metrics (yet), but usages of deferredFinally() are extremely rare.