Fix: Debian 11 Bullseye is deprecated, remove it

[hoh]

Debian 11 provided Python 3.9.

This branch removes the support for both Debian 11 and Python 3.9. The oldest distribution supported is now Ubuntu 22.04 with Python 3.10.

That that mentions of Debian 11 were replaced in
some example files that were not maintained and
the change has not been tested. These remain to
serve as examples for developers.

Explain what problem this PR is resolving

Related ClickUp, GitHub or Jira tickets : ALEPH-XXX

Self proofreading checklist

• The new code clear, easy to read and well commented.
• New code does not duplicate the functions of builtin or popular libraries.
• An LLM was used to review the new code and look for simplifications.
• New classes and functions contain docstrings explaining what they provide.
• All new code is covered by relevant tests.
• Documentation has been updated regarding these changes.

Changes

Explain the changes that were made. The idea is not to list exhaustively all the changes made (GitHub already provides a full diff), but to help the reviewers better understand:

• which specific file changes go together, e.g: when creating a table in the front-end, there usually is a config file that goes with it
• the reasoning behind some changes, e.g: deleted files because they are now redundant
• the behaviour to expect, e.g: tooltip has purple background color because the client likes it so, changed a key in the API response to be consistent with other endpoints

How to test

Explain how to test your PR.
If a specific config is required explain it here (account, data entry, ...)

Print screen / video

Upload here screenshots or videos showing the changes if relevant.

Notes

Things that the reviewers should know: known bugs that are out of the scope of the PR, other trade-offs that were made.
If the PR depends on a PR in another repo, or merges into another PR (i.o. main), it should also be mentioned here

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.67%. Comparing base (1c888e2) to head (99b34ba).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #693      +/-   ##
==========================================
- Coverage   62.72%   62.67%   -0.05%     
==========================================
  Files          69       69              
  Lines        6069     6069              
  Branches      642      642              
==========================================
- Hits         3807     3804       -3     
- Misses       2110     2113       +3     
  Partials      152      152              

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[hoh]

Test failures appear to be related to the expectation of having Debian 11 droplets, which should not be the case anymore.