Changes proposed in this Pull Request

Since #1613, the files era5-HDD-per-country.csv and era5-runoff-per-country.csv are intended to be part of the data bundle hosted on Zenodo. This PR adds them to the datafiles list in the retrieve.smk rule to ensure they are correctly downloaded and used as inputs of downstream rules such as build_hydro_profile.

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.