Allow for port range configuration

[LVala]

I changed credo config, as it complains about the Priv.ICEAgent.new which is not complex at all imo.

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 80.09%. Comparing base (e9bf93d) to head (83ea750).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
+ Coverage   78.99%   80.09%   +1.09%     
==========================================
  Files          25       25              
  Lines        1419     1422       +3     
==========================================
+ Hits         1121     1139      +18     
+ Misses        298      283      -15     

Files	Coverage Δ
lib/ex_ice/ice_agent.ex	54.68% <ø> (ø)
lib/ex_ice/priv/ice_agent.ex	83.94% <100.00%> (+1.79%)	⬆️
lib/ex_ice/priv/gatherer.ex	93.02% <85.71%> (-2.10%)	⬇️

... and 1 file with indirect coverage changes

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