[stable22] Allow user to delete their keys

[backportbot-nextcloud[bot]]

:warning: This backport had conflicts and is incomplete :warning:

backport of #305

[codecov[bot]]

Codecov Report

Merging #308 (9d58b5b) into stable22 (00f48da) will increase coverage by 0.02%. The diff coverage is n/a.

@@              Coverage Diff               @@
##             stable22     #308      +/-   ##
==============================================
+ Coverage       94.54%   94.57%   +0.02%     
- Complexity         40       48       +8     
==============================================
  Files               3        3              
  Lines             110      129      +19     
==============================================
+ Hits              104      122      +18     
- Misses              6        7       +1     

Impacted Files	Coverage Δ
apps/testing/lib/Controller/LockingController.php	91.89% <0.00%> (-1.86%)	:arrow_down:
apps/files_trashbin/lib/Sabre/PropfindPlugin.php	97.14% <0.00%> (+0.47%)	:arrow_up:
apps/dav/lib/Connector/Sabre/LockPlugin.php	94.73% <0.00%> (+0.98%)	:arrow_up:

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