Add industry sites

[toniseibold]

Closes # (if applicable).
PyPSA/pypsa-de#8

Changes proposed in this Pull Request

This PR uses the dataset provided by Neuwirth et al. to add existing industry sites.
Where necessary this dataset is complemented with other datasets since it's limited to EU27 countries only.

Ammonia

As soon as the config setting config["sector"]["ammonia"] is either True or regional and the optimization runs with perfect or myopic foresight, ammonia plant capacities are added in add_existing_baseyear.

Switching existing Haber-Bosch capacities from natural gas to hydrogen is not permitted since it's associated with retrofitting costs and there are only few Examples.
Comparison of eurostat demand vs. database installed capacity shows a high degree of agreement.

Checklist

• I tested my contribution locally and it works as intended.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in config/config.default.yaml.
• Changes in configuration options are documented in doc/configtables/*.csv.
• Sources of newly added data are documented in doc/data_sources.rst.
• A release note doc/release_notes.rst is added.