Accept label action for PR and issues

[xinyuluo]

Description of the task

Label action in PR and issues are now accepted.

How to test

In mock_payloads, one can find pull_request.labeled_two_labels.json and issues.labeled.json.

To test that label action is now accepted, run the following commands:

./notabot check --json path/to/file

The expected output for the above two json files should be:

Using push routing:  
  backend/api* -> #aa
  backend/megaindex* or backend/ahrefskit* -> #backend
  any -> #all-push-events
Using pull request routing:
  backend* -> #backend
  aa* -> #aa-git
  siren* -> #siren
  not backend* or aa* or siren* -> #frontend-bot

with url(s) containing information about the PR/issue and its new labels.