Sharing of representative datasets via compressed Zarr zips

[VeckoTheGecko]

I realised that there is both a better approach to #2510, as well as a way that we can pave the way for Parcels-code/parcels-benchmarks#40 ("Future work: better testing").

This PR adds tooling and documentation that allows users to easily share datasets via the issue tracker. These datasets will be first trimmed of redundant array data, then shared as Zipped zarr files using zarr.storage.ZipStore.

This allows people to easily share their datasets - including the mesh itself - directly via GitHub (which has an upload limit of 25Mb for zips). Working with the MOI grid data in parcels-benchmarks the resulting dataset was only 26Mb (i.e., the glamf and glamu).

This PR also removes the old JSON approach as it is no longer needed.

• xref Update fieldset ingestion to use convert modules parcels-benchmarks#40
  • This is a significant step in this direction
• Tests added
• This PR targets the correct branch (main for normal development, v3-support for v3 support)

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
  • Describe how you used it (e.g., by pasting your prompt): Used it to update the docs (pointing it to the old docs, then to an example usecase) then made manual copy edits.

[VeckoTheGecko]

Docs:

[erikvansebille]

Looks very good, a few comments below