notification panel: rework time formatting (#8997)

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

---------

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

crates/collab_ui/src/chat_panel.rs

@@ -493,9 +493,10 @@ impl ChatPanel {
                                 )
                                 .child(
                                     Label::new(time_format::format_localized_timestamp(
-                                        OffsetDateTime::now_utc(),
                                         message.timestamp,
+                                        OffsetDateTime::now_utc(),
                                         self.local_timezone,
+                                        time_format::TimestampFormat::EnhancedAbsolute,
                                     ))
                                     .size(LabelSize::Small)
                                     .color(Color::Muted),