Add WithDialOptions option

[bradleyjkemp]

Fixes #69

[codecov]

Codecov Report

Merging #71 into master will decrease coverage by 0.25%.
The diff coverage is 25%.

@@            Coverage Diff             @@
##           master      #71      +/-   ##
==========================================
- Coverage   56.81%   56.55%   -0.26%     
==========================================
  Files          31       31              
  Lines        1167     1174       +7     
==========================================
+ Hits          663      664       +1     
- Misses        400      406       +6     
  Partials      104      104

Flag	Coverage Δ
#integration	55.96% <25%> (-0.25%)	⬇️
#unit	18.84% <0%> (-0.4%)	⬇️

Impacted Files	Coverage Δ
grpc-proxy/proxy.go	54.79% <ø> (ø)	⬆️
grpc-proxy/config.go	37.77% <0%> (-5.82%)	⬇️
grpc-proxy/grpc_handler.go	61.61% <100%> (+0.39%)	⬆️

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