Exclude bot activity from UI

Split out from #344674 (closed), though I see quite some conceptual overlap...

Release notes

You can now mark users as bots and exclude their activity from the GitLab UI.

Problem to solve

We have a couple of bot users that push to repositories, create issues or update Merge Requests.

These users pollute some views like Activity, Commits or Contributors.

It would be great to mark such bot users and allow us to exclude them in these views.

Proposal

New bot flag in profile

Filter in Activity view

Intended users

Metrics