Support clang 16 in docker CI

[godexsoft]

Fixes #1175

• Adds clang-16 as a secondary compiler to the docker CI image
• Slightly improves how gcc-12 is integrated
• Sets up the CI to make use of clang and run tests compiled by it alongside gcc's build
• These are not the robots you are looking for

Currently clang-tidy is producing a lot of interesting output. But i think this can be handled outside of this PR now.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 64.44%. Comparing base (1fe42c8) to head (1fd2018).

❗ Current head 1fd2018 differs from pull request most recent head d6ce1f9. Consider uploading reports for the commit d6ce1f9 to get more accurate results

Files	Patch %	Lines
src/etl/impl/LedgerLoader.hpp	0.00%	2 Missing ⚠️
src/etl/impl/SubscriptionSource.cpp	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1348      +/-   ##
===========================================
+ Coverage    64.38%   64.44%   +0.05%     
===========================================
  Files          248      248              
  Lines        10544    10544              
  Branches      5839     5839              
===========================================
+ Hits          6789     6795       +6     
+ Misses        1920     1914       -6     
  Partials      1835     1835              

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[kuznetsss]

Really good improvements 👍 Just a few comments.

[kuznetsss]

Looks good 👍