purge influx feature

[FabianHofmann]

Closes #212
Touches #211

Change proposed in this Pull Request

Initial attempt was to solve #211, but is turns out to be tricky. The problem is that the era5 module relies on get_ functions which take the era5 retrieval parameters as an argument. The SolarPosition function however requires a dataset with the complete set of coordinates. It would be necessary to pass the cutout.data as an argument to the get_solar_position function. This requires changes one have to think through a bit.
The same counts for the sarah module. Its get_data function does not use the feature argument so far. It would be necessary to make separate get_influx and get_solar_position functions. I would postpone that change to another time.

In order to make the influx feature still a bit handier, I removed the solar athmospheric insolation variable from the influx feature as well as from the SolarPosition function. The variables were renamed to solar_azimuth and solar_altitude.

Motivation and Context

Make the influx feature leaner. Make data variables accessible via cutout.data.solar_altitude/ cutout.data.solar_azimuth

How Has This Been Tested?

No test added.

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 change)

Checklist

• I tested my contribution locally and it seems to work fine.
• I locally ran pytest inside the repository and no unexpected problems came up.
• I have adjusted the docstrings in the code appropriately.
• I have documented the effects of my code changes in the documentation doc/.
• I have added newly introduced dependencies to environment.yaml file.
• I have added a note to release notes doc/release_notes.rst.
• I have used pre-commit run --all to lint/format/check my contribution

[codecov-commenter]

Codecov Report

Merging #222 (5f5efe3) into master (6c69d51) will increase coverage by 0.16%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #222      +/-   ##
==========================================
+ Coverage   72.34%   72.50%   +0.16%     
==========================================
  Files          19       19              
  Lines        1580     1575       -5     
  Branches      222      221       -1     
==========================================
- Hits         1143     1142       -1     
+ Misses        371      368       -3     
+ Partials       66       65       -1     

Impacted Files	Coverage Δ
atlite/datasets/sarah.py	25.53% <0.00%> (ø)
atlite/pv/irradiation.py	67.08% <60.00%> (ø)
atlite/convert.py	67.02% <100.00%> (ø)
atlite/datasets/era5.py	89.79% <100.00%> (ø)
atlite/pv/solar_position.py	100.00% <100.00%> (+8.88%)	⬆️

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[euronion]

I didn't test it, in general it LGTM. Thanks! :)