Refactor event handler

- Break down the EventServer.handleEvent() implementation into multiple
  smaller functions which are extensively tested on their own.
  - New implementation of filter Alerts for Event
  - New implementation of Event matches Alert
- Remove any readiness check on Alert or Provider.
- Convert the event handler test from controllers/ dir to work with
  just EventServer without any reconciler, keeping all the test cases
  and slightly modified test set up code.

Signed-off-by: Sunny <darkowlzz@protonmail.com>