Update filter to TCO20 and TCO21

When group have events in challengeFilter, call API with events instead groupId.

Please ref. swagger file: https://github.com/topcoder-platform/challenge-api/blob/4a480a0e7c435a6e3d431fdfa03960bf3ce91455/docs/swagger.yaml#L184-L191

example:

"challengeFilter": {
    "events": ["tco21"]
  },

Final Submission Guidelines

Git issue link: https://github.com/topcoder-platform/community-app/issues/5056