Feat/ekh 1 0 0

[Oisin-M]

Description

Update earthkit-hydro to use v1.0.0 onward and links to the readthedocs.

Contributor Declaration

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• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[sandorkertesz]

@Oisin-M , thanks for this update. I suggest you change the earthkit-hydro link in docs/conf.py too.