One way to change freq for map processing

[dulte]

Change Summary

Made it so when ModelMapsEngine is run, main_freq is changed to maps_freq. If maps_freq=coarsest, then the coarsest freq of the given freqs are chosen

Related issue number

Proposed fix to #1260

Checklist

• Start with a draft-PR
• The PR title is a good summary of the changes
• PR is set to AeroTools and a tentative milestone
• Documentation reflects the changes where applicable
• Tests for the changes exist where applicable
• Tests pass locally
• Tests pass on CI
• At least 1 reviewer is selected
• Make PR ready to review

[codecov]

Codecov Report

Attention: Patch coverage is 78.57143% with 6 lines in your changes missing coverage. Please review.

Project coverage is 79.00%. Comparing base (89b9921) to head (8363456).
Report is 1 commits behind head on main-dev.

Files	Patch %	Lines
pyaerocom/aeroval/modelmaps_engine.py	60.00%	4 Missing ⚠️
pyaerocom/aeroval/_processing_base.py	88.88%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           main-dev    #1312   +/-   ##
=========================================
  Coverage     79.00%   79.00%           
=========================================
  Files           136      136           
  Lines         20797    20812   +15     
=========================================
+ Hits          16430    16443   +13     
- Misses         4367     4369    +2     

Flag	Coverage Δ
unittests	79.00% <78.57%> (+<0.01%)	⬆️

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[lewisblake]

Based on our discussion I think we approach the other way. 😸