Update the global notification dropdrown to use htmx (#3836)

- Loads the notification items only after clicking on the bell icon
- This reduces ~30 db queries, on every page load
- The activities display are also on the most costly db queries, on a
simple test db the time spent on processing sql reduces from ~530ms to
~150ms
- The side-effect of ajax based request is the whenever the bell icon is
  clicked it will always display the latest data and not stale, even if
the page is not refreshed.

Fixes #3806