Improved display of TaskModel hierarchy in TaskModelAdmin object page

[Skrattoune]

This adds the possibility to see for each task if it has parent and children tasks
My sub tasks often have subtasks, and with the current version of the admin, I'm pretty blind

No big changes, no impact on testing...
not depending on anything else
Working for some time now on my server

I think it is ready to make it to the official repository

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.36%. Comparing base (2d37f25) to head (9f4ac9c).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #142      +/-   ##
==========================================
- Coverage   67.95%   66.36%   -1.60%     
==========================================
  Files          36       36              
  Lines         749      764      +15     
  Branches       88       89       +1     
==========================================
- Hits          509      507       -2     
- Misses        240      257      +17     

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[Skrattoune]

Ready to be reviewed and integrated to main