Support new CDS package (potential successor to `cdsapi`)

[euronion]

More information here: https://forum.ecmwf.int/t/new-cdsapi-version-0-7-7-released-and-new-api-package-for-advanced-users-ready-to-be-used/12806

• See if the package offers better functionality or performanace
• See if migration from cdsapi to the package is possible and what is involved
• Implement the package, either as alternative to cdsapi or as substitute