Processor service: Event processing issues fix attempt 3

[iLLiCiTiT]

Changelog Description

Another attempt to fix issues with processor service that pretends to process events, but not doing anything.

Additional info

If event hub finds out it is diconnected, it does not try to get more events and stops the loop.
Added option to discover event handler classes without having register method in the file -> this might help to avoid garbage collection of handler objects ??? possible cause 1 on range 0-10 ???.

More context

Processor still prints "Processing event" message, so it does fetch AYON events, but either ftrack connection does not exist, or subscribers are not available anymore.

Testing notes:

1. Keep it running in production for few days.
2. Validate if processor pretends to process events but in fact does not.