Enable filtering of added rules via knobs in Settings

[kalmarek]

This works for KBIndex only (and will stay like this)

• document the feature.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 8 lines in your changes missing coverage. Please review.

Project coverage is 94.90%. Comparing base (f8e65d9) to head (6dc2632).

Files	Patch %	Lines
src/knuthbendix_idxA.jl	80.76%	5 Missing ⚠️
src/knuthbendix2.jl	75.00%	2 Missing ⚠️
src/rewriting.jl	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
+ Coverage   94.80%   94.90%   +0.09%     
==========================================
  Files          30       30              
  Lines        1829     1883      +54     
==========================================
+ Hits         1734     1787      +53     
- Misses         95       96       +1     

Flag	Coverage Δ
unittests	94.90% <90.90%> (+0.09%)	⬆️

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