Feature/add dewpoint temperature

Closes # (if applicable).

Change proposed in this Pull Request

Adds dewpoint temperature to the list of features fetched from ERA5.

It is possible that existing data pipelines that expect only 2 variables for the temperature may experience breaks with the addition of the new column. Should this new feature be optional instead ?

Description

Added the dewpoint_temperature variable, consistent with the processing of existing temperature and soil temperature variables

Motivation and Context

Dewpoint temperature is a good indicator of climate comfort and predictor of electricity demand.

How Has This Been Tested?

Tested by preparing a Cutout from ERA5, verifying the dew point temperature is included. Tested on python 3.10.12

Type of change

[ ] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

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

PyPSA / atlite