fix: udpate lxd docs paths

[minaelee]

Updates LXD documentation paths to use the docs version corresponding to the current LTS release, and to remove the no-longer-used /en/ part of the path.
Also fixes a link in https://canonical.com/lxd/install - the link for "Learn more about LXD and security" was pointing to the docs on containers and VMs instead of the security docs.

[webteam-app]

minaelee is not a collaborator of the repo

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.79%. Comparing base (d1f8f23) to head (63bbf1d).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2447   +/-   ##
=======================================
  Coverage   78.79%   78.79%           
=======================================
  Files          16       16           
  Lines        1849     1849           
=======================================
  Hits         1457     1457           
  Misses        392      392           

Flag	Coverage Δ
python	78.79% <ø> (ø)

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