Remove unreachable/invalid commits related entries from activity feed
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### Proposal
Do not list in the profile activity feed (or delete the activity entries) for the following:
- commits that are unreachable or dangling
- commits that have invalid hashes (ie: the one where https://gitlab.com/\<username\>/\<project\>/-/commit/\<commit hash\> displays a 404 Git Resource Not Found)
_note : this proposal may be extended to any object (blob, tree, branch, etc) that is unreachable or with invalid hash_.
_note 2: in case dangling objects may have some uses, we can just consider the ones with invalid hashes_.
### Steps to reproduce
1. create repo
2. make some commits and push
3. introduce a dangling commit and force push
4. run **housekeeping** and **Prune Unreachable Objects**
5. make sure the commit hash return a 404 (using https://gitlab.com/\<username\>/\<project\>/-/commit/\<commit hash\>)
6. go to the profile and still see the entry related to the commit with a now invalid hash
@gitlab-bot label ~"user profile"
issue