Fail zarr format specification requirements if format cannot be inferred

[leifdenby]

Describe your changes

There are a few things about the current zarr format requirement checks that are brittle:

• If we can't open the underlying zarr store to infer the version we default to 2. I think it would be better for the requirement to fail here. It doesn't make sense to have something as a requirement if we don't verify if the requirement is satisfied or not
• we want the validation function to be able to take a xr.Dataset to apply validation too, but unfortunately xarray does not set the storage_options arguments anywhere on the xr.Dataset it returns when xr.open_zarr() / xr.open_dataset() is called to open the dataset. These storage_options are needed when we want to access the underlying store. As a hack the cli sets the storage-options on ds.encoding['storage_options']. With this PR we now warn the caller if storage_options isn't defined on ds.encoding if the zarr format requirement checks fail to find out either what the zarr version is or whether there is consolidated metadata.

The motivation here is two-fold: 1) ensure that we are actually checking for the things the spec requires and 2) nudge the user to supply storage_options on the provided xr.Dataset.

No change of dependencies required.

Issue Link

Partially resolves #2

Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality, e.g. adding a new dataset)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected, e.g. removing or moving a dataset in the catalog)
• 📖 Documentation (Addition or improvements to documentation)
• 🔨 Maintenance (Fixing issues with CI/CD and changes to upstream dependencies)

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[franchg]

lgtm!