Add Kubernetes service connection as data source

[beschoenen]

I was missing this data source, since the authentik helm chart comes with a service connection out of the box.

[codecov]

Codecov Report

Attention: Patch coverage is 74.07407% with 14 lines in your changes missing coverage. Please review.

Project coverage is 80.19%. Comparing base (217db6e) to head (0b5c412).
Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
...rnal/provider/data_source_outpost_sc_kubernetes.go	73.58%	13 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #577      +/-   ##
==========================================
- Coverage   80.28%   80.19%   -0.09%     
==========================================
  Files          96       97       +1     
  Lines       10753    10807      +54     
==========================================
+ Hits         8633     8667      +34     
- Misses       1665     1682      +17     
- Partials      455      458       +3     

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