[#2914] Add certificate manager to admin index

[pi-sigma]

Taiga: https://taiga.maykinmedia.nl/project/open-inwoner/issue/2914

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.31%. Comparing base (7989d35) to head (f11b46f).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1512   +/-   ##
========================================
  Coverage    94.31%   94.31%           
========================================
  Files         1068     1068           
  Lines        40386    40386           
========================================
  Hits         38089    38089           
  Misses        2297     2297           

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