Add ability to skip applying rules

[davidhuie-dd]

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PR Summary

This introduces a skip_rules configuration setting which prevents go-audit from setting rules itself. This enables audit rules to be set by an external system, utilizing go-audit exclusively for logging.

[codecov-io]

Codecov Report

Merging #61 into master will decrease coverage by 0.1%.
The diff coverage is 25%.

@@            Coverage Diff            @@
##           master     #61      +/-   ##
=========================================
- Coverage   75.21%   75.1%   -0.11%     
=========================================
  Files           5       5              
  Lines         476     478       +2     
=========================================
+ Hits          358     359       +1     
- Misses        101     102       +1     
  Partials       17      17

Impacted Files	Coverage Δ
audit.go	74.68% <25%> (-0.21%)	⬇️

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[davidhuie-dd]

Is anyone checking these?

[CLAassistant]

All committers have signed the CLA.

[nbrownus]

👋 @davidhuie-dd thanks for the PR! This looks like a good idea to me but I'd like to modify it a bit. rules.skip seems more natural, can you also update the example config with a little comment about the additional option?