prototype "before retry action" support

[Ladicek]

Interesting idea from https://quarkusio.zulipchat.com/#narrow/stream/187030-users/topic/fault.20tolerance.20using.20.40Retry.20annotation

It would be nice to support running arbitrary user-provided code before each and every retry attempt.

API-wise, it could be another attribute on the already overcrowded @Retry annotation, or it could be a CDI event (as those are processed synchronously).

[hbelmiro]

I created #485 with an initial implementation.