ci: Support more flexible strategy matrix generation

[bthomee]

High Level Overview of Change

This change replaces the strategy matrix generation process by a fully typed and test Python implementation. This also enables more flexibility for adjusting or extending the functionality as needed.

Context of Change

The current Python script reads JSON files that contain the definitions to generate the strategy matrix from. The script does too many things at once, which makes it hard to read. The code is also not tested.

The change in this PR refactors the strategy matrix generation, such that:

• Data types are used to express the configurations and are validated, such that mistakes more difficult or even impossible to make.
• The functions and data types are fully tested.
• Basic support is added for publishing packages and images, as well as for sanitizers. Their actual implementations will come in a follow-up PR.
• Per separate discussions with @Bronek a while back, the configurations to run for commits, merges, and schedules have been adjusted to focus on key configurations, while reducing duplication.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.0%. Comparing base (40198d9) to head (9de4bca).

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #6160     +/-   ##
=========================================
+ Coverage     79.1%   80.0%   +0.9%     
=========================================
  Files          836     836             
  Lines        71245   74413   +3168     
  Branches      8322    8293     -29     
=========================================
+ Hits         56356   59514   +3158     
- Misses       14889   14899     +10     

see 500 files with indirect coverage changes

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