Date time columns "with no time zone" in merge request
**Proposal**
Set `merge_request_metrics.merged_at` to be timezone sensitive.
The following discussion from !107998 should be addressed:
- [ ] @morefice started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/107998#note_1250263021): (+2 comments)
> **note:** Too bad `merged_at` is not timezone sensitive in `merge_request_metrics` :cry:
issue