Provide a general WMS verify certificate option

[jwkaltz]

Provide a general WMS verify certificate option, for cantonal setups where all WMS are served with self-signed certificates

Improves #2005 , tested in canton Jura infrastructure.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.51%. Comparing base (87b1062) to head (c2f1a4d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2034   +/-   ##
=======================================
  Coverage   85.51%   85.51%           
=======================================
  Files         120      120           
  Lines        5276     5276           
=======================================
  Hits         4512     4512           
  Misses        764      764           

Flag	Coverage Δ
unittests	85.51% <ø> (ø)

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