Follow up of #7994 to rework the notification panel timestamps.
This PR also includes some of the changes @evrsen proposed in #8996 
Here is what it looks like now:


https://github.com/zed-industries/zed/assets/53836821/d85450e7-eab6-4fe7-bd11-1d76c0e87258

Release Notes:
- Reworked date time formatting in the chat and the notification panel
- Added hover style to notifications and hovering tooltip on timestamps

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Co-authored-by: Evren Sen <146845123+evrsen@users.noreply.github.com>