Review request: Manual sorting of activities (Bug 405033)

Hi all,

Requesting review and coordination in merging the activity sorting 
feature as described in: Bug 405033 
<https://bugs.kde.org/show_bug.cgi?id=405033> "Manual sorting of activities"
This feature gives users the ability to reorder their activities 
manually within the activities KCM. The order is then propagated to the 
various applets.

Happy to address any issues or feedback received!

## Dependent MRs

- plasma-desktop#3185 - 
https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/3185
   - Includes a demo video
- plasma-activities#64 - 
https://invent.kde.org/plasma/plasma-activities/-/merge_requests/64
- kactivitymanagerd#109 - 
https://invent.kde.org/plasma/kactivitymanagerd/-/merge_requests/109
   - Note: This reverts the previous revert in MR #91.
- plasma-workspace#5986 - 
https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/5986

## Already Merged
- kactivitymanagerd#91 [Reverted] - 
https://invent.kde.org/plasma/kactivitymanagerd/-/merge_requests/91 
<https://invent.kde.org/plasma/kactivitymanagerd/-/merge_requests/91)~~>

Thank you in advance

-- 
daryl