Fix for HA server deletion

[enrichman]

This PR fixes #468 when deleting a server with a name that contains a - was not handled properly.

The Cluster name is now fetched from the owner of the StatefulSet.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.66667% with 37 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.18%. Comparing base (5c95ca3) to head (2e928ee).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/controller/cluster/statefulset.go	49.31%	31 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #493      +/-   ##
==========================================
+ Coverage   54.04%   54.18%   +0.13%     
==========================================
  Files          56       56              
  Lines        6528     6554      +26     
==========================================
+ Hits         3528     3551      +23     
- Misses       2734     2739       +5     
+ Partials      266      264       -2     

Flag	Coverage Δ
cli	51.68% <42.66%> (+0.21%)	⬆️
controller	54.01% <50.66%> (+0.20%)	⬆️
e2e	54.01% <50.66%> (+0.20%)	⬆️
unit	40.67% <2.66%> (-0.16%)	⬇️

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