Refactored native model fixes by adding common base class NativeDatasetFix

[schlunma]

Description

This PR simplifies native model fixes by adding a base class NativeDatasetFix with common operations necessary for almost all datasets. This will dramatically simplify #1678.

Closes #1690

Link to documentation: https://esmvaltool--1694.org.readthedocs.build/projects/ESMValCore/en/1694/develop/fixing_data.html#fix-native-data

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[codecov]

Codecov Report

Merging #1694 (803f4e8) into main (76c9ffa) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1694      +/-   ##
==========================================
+ Coverage   91.49%   91.51%   +0.01%     
==========================================
  Files         204      205       +1     
  Lines       11174    11191      +17     
==========================================
+ Hits        10224    10241      +17     
  Misses        950      950              

Impacted Files	Coverage Δ
esmvalcore/cmor/_fixes/emac/_base_fixes.py	100.00% <100.00%> (ø)
esmvalcore/cmor/_fixes/emac/emac.py	100.00% <100.00%> (ø)
esmvalcore/cmor/_fixes/icon/_base_fixes.py	100.00% <100.00%> (ø)
esmvalcore/cmor/_fixes/icon/icon.py	100.00% <100.00%> (ø)
esmvalcore/cmor/_fixes/native_datasets.py	100.00% <100.00%> (ø)

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[schlunma]

I have no idea why that Codacy error (Django was not configured. For more information run pylint --load-plugins=pylint_django --help-msg=django-not-configured) appears here. I think we can simply ignore it...

[remi-kazeroni]

Thanks for your contribution @schlunma! The code looks good to me. This should help lowering the bar to add support for native model output in the future. This is also a good step towards reducing code duplication w.r.t. model fixes. The CMORization of models related to this PR gives identical results to that of the main branch and other models are not affected (different classes) so I think this is ready to be merged 👍

[remi-kazeroni]

I have no idea why that Codacy error (Django was not configured. For more information run pylint --load-plugins=pylint_django --help-msg=django-not-configured) appears here. I think we can simply ignore it...

I have seen that in some other unrelated PRs as well, so I would agree...

[schlunma]

Awesome, thanks for the review @remi-kazeroni ! 🚀