Add Webhooks for Releases

Problem to solve

There is no way of triggering something external when a new release is created.

This could also compete with the deployment_notfier CI Orb and webhook CI Orb

Proposal

In the Settings > Integrations page of a project, we have different kind of webhook triggers for push, comments, issues, pipelines, ... It would be very convenient to also have a trigger for new releases, and when they are deployed (pipeline for release tag completed

• trigger webhooks when release is created.
• add "Releases events" to Settings > Integrations page of a project
• add "Releases events" to group integrations setting page

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