Set handler formatter in FIlterHandler

[orlandothoeny]

Currently the FilterHandler does not allow setting the formatter of the handler it uses.
Of course one could first set the formatter in the handler that should be used, then pass it to the FilterHandler.

However in my current use case it would be preferable if the FilterHandler would override the setFormatter method of the AbstractHandler. My current use case: Using the Monolog Drupal module to log Drupal log messages. I want to only log a range of levels. (Info - Warning to stdout, Error and up to stderr).
The Drupal Monolog module currently uses setFormatter to set a formatter.

Don't know if this is good design, maybe this should be handled by the Drupal module. Input appreciated.

--
Ah, I've just seen that the Drupal module uses the 1.x version of Monolog.
And that the FilterHandler does not implement FormattableHandlerInterface.

[orlandothoeny]

PR #1387