add parameters to manage opn-cli CA file

[fraenki]

This PR adds the following:

• create the opn-cli config directory
• either symlink opn-cli ca file to system-wide ca file
• or create opn-cli ca file with custom content
• parameters to enable/disable every aspect of this functionality
• unit tests
• a new entry in README

[codecov]

Codecov Report

Merging #11 (29e1e4e) into main (6619cd6) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##              main       #11   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          273       277    +4     
=========================================
+ Hits           273       277    +4     

Impacted Files	Coverage Δ
lib/puppet/provider/opnsense_provider.rb	100.00% <0.00%> (ø)

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