feat: implement entropy pre-filtering to optimize secret detection

[oittaa]

Split out from #1467

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Codecov Report

❌ Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.32%. Comparing base (1216c9b) to head (6724795).
⚠️ Report is 168 commits behind head on master.

Files with missing lines	Patch %	Lines
rules/hardcoded_credentials.go	40.00%	5 Missing and 1 partial ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1479      +/-   ##
==========================================
+ Coverage   68.49%   69.32%   +0.82%     
==========================================
  Files          75       82       +7     
  Lines        4384     6601    +2217     
==========================================
+ Hits         3003     4576    +1573     
- Misses       1233     1799     +566     
- Partials      148      226      +78     

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[oittaa]

I made the educated guess that strings shorter than 8 characters can never hit the default entropy requirements from Zxcvbn without testing too much.

This could be improved further with Shannon entropy filtering before the much more advanced and heavier Zxcvbn. More info: #1472