[Security] Document how to wire up a custom authentication success handler

[xabbuh]

From symfony/symfony#20912:

I was trying to implement a custom authentication success handler, and it took me quite a bit to identify how to inject the options, the fact that it's based on the existence of a setOptions method is rather opaque.

Can we have an interface that is implemented by official handlers exposing setOptions?

This feature was introduced in Symfony 2.6 (see symfony/symfony#11993).

[javiereguiluz]

Closing as fixed by #10423. Instead of doing this, we've decided to promote Guard Authenticators as much as possible.