Allow to configure retry policy on a per-task basis

[nishiol]

Based on discussion: #737

Similar PR: #739

Allows to configure retry policy on per-task basis in programmatic way. No db migrations needed.
Usage example can be found in README.md

@lburja could you please also take a look at this PR?

[lburja]

The ideea looks interesting. The upside is that DB changes are not needed, and there is flexibility in applying different strategies. The downside is that you need to implement a specific interface.

I didn’t review in detail at the code, but from what I can tell, the idea should work

[nishiol]

Yes, it's kind of tight coupling. But if this a problem, it could be avoided by creating an implementing class in the module which depends on transaction-outbox stuff. It'll look like some wrapper around your business logic class which you want to be called by transaction-outbox.