More options for event types on Slack integration
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=15516) </details> <!--IssueSummary end--> Currently it sends to Slack many events we do not need to be spammed about. E.g. we jsut need to know about issues create, merge requests close or only commits to the master. Will be nice to have options to filter by many possible combinations.
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