Add july hackathon and move calendar into service

Arianna Haradonrequested to merge
gitlab-community/gitlab-org/developer-relations/contributor-success/contributors-gitlab-com:create-calendar-service into main

What does this MR do and why?

Add july hackathon and move calendar into service

Screenshot_2025-05-21_at_1.24.45_PM

Validation steps

/cc @leetickett-gitlab

Edited by Arianna Haradon

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