Restore Hackathon Label processor for Q2 Hackathon

Restores the HackathonLabel processor for the Q2 Hackathon on 2021-06-02 to 2021-06-03.

Please see the details in https://about.gitlab.com/community/hackathon/ and https://gitlab.com/gitlab-com/marketing/community-relations/contributor-program/hackathon/-/issues/52