[feat] Facilitate local imports from configuration files

[vkarak]

This is the exact equivalent of loading test library module from a test file. Now users can import custom modules that reside in the same directory as the configuration file, without having to resort to boilerplate code that updates sys.path.

Close #2877.

Implementation details

Since the functionality is exactly the same as that for the test files, the code is refactored so as to be reused i both scenarios.

Note that the interface import_module_from_file() has changed, however we sill schedule this change for 4.9, since our versioning reflects the test API and not the API of the various utilities.

Todos

• Update documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.22%. Comparing base (8000b58) to head (92800e3).
⚠️ Report is 6 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3548      +/-   ##
===========================================
- Coverage    91.23%   91.22%   -0.02%     
===========================================
  Files           62       62              
  Lines        13464    13470       +6     
===========================================
+ Hits         12284    12288       +4     
- Misses        1180     1182       +2     

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