docs: update doc with eccc-fstd, cdsapi and regrid

[chebertpinard]

Description

Recent change were made in the anemoi-datasets sources to support ECCC standard format files and allow external user to download ERA5 data using the CDS API. Additionally, a filter was added to interpolate the retrieved data on an arbitrary grid. These changes haven't been documented yet. This PR doesn't modify the code, it only provides a description for these change in the documentation.

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 not work as expected)
• Documentation update

Issue Number

Code Compatibility

• I have performed a self-review of my code

Code Performance and Testing

• I have added tests that prove my fix is effective or that my feature works
• I ran the complete Pytest test suite locally, and they pass

Dependencies

• I have ensured that the code is still pip-installable after the changes and runs
• I have tested that new dependencies themselves are pip-installable.

Documentation

• My code follows the style guidelines of this project
• I have updated the documentation and docstrings to reflect the changes
• I have added comments to my code, particularly in hard-to-understand areas

Additional Notes

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📚 Documentation preview 📚: https://anemoi-datasets--201.org.readthedocs.build/en/201/