[stable8] docs: Move to more outline icons

[backportbot]

Backport of #7860

Warning, This backport's changes differ from the original and might be incomplete ⚠️

Todo

• Review and resolve any conflicts
• Amend HEAD commit to remove the line stating to skip CI

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[nickvergessen]

tabbing indent was off in NcAppNavigation.vue so the patch did not apply cleanly there. Redid that.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.08%. Comparing base (6599ab0) to head (6a1f881).
⚠️ Report is 2 commits behind head on stable8.

Additional details and impacted files

@@           Coverage Diff            @@
##           stable8    #7861   +/-   ##
========================================
  Coverage    45.08%   45.08%           
========================================
  Files          191      191           
  Lines         4749     4749           
  Branches      1226     1226           
========================================
  Hits          2141     2141           
  Misses        2512     2512           
  Partials        96       96           

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