Optimise VariantValidator caching and document configuration

[Peter-J-Freeman]

No description provided.

[Peter-J-Freeman]

Clean commit to replace the pull request #877
The old request is still open as it contains the profiling info. @John-F-Wagstaff.

The code is cleaned, cache settings moved to the settings.py so they can easily be adapted and toggled on and off, including using Environment Variables

[codecov]

Codecov Report

❌ Patch coverage is 96.07843% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.89%. Comparing base (650b73a) to head (534a662).
⚠️ Report is 3 commits behind head on regex_removal.

Files with missing lines	Patch %	Lines
VariantValidator/modules/vvMixinConverters.py	66.66%	1 Missing ⚠️
VariantValidator/modules/vvMixinInit.py	94.11%	1 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                @@
##           regex_removal     #880      +/-   ##
=================================================
+ Coverage          84.84%   84.89%   +0.05%     
=================================================
  Files                 48       48              
  Lines              14554    14586      +32     
=================================================
+ Hits               12348    12383      +35     
+ Misses              2206     2203       -3     

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[John-F-Wagstaff]

We probably want a default setting here, or to not set at all (and rely on the vvhgvs default) and only set to 0 when we override it to 0 explicitly, otherwise we just flipped the default from 100 to 0.