Loaders for MuData-Zarr

[keller-mark]

Fixes #1119

Depends on scverse/mudata#7

Change List

• Add MuDataSource class and mudata-*.zarr file types.
  • Can re-use the options schemas from anndata-*.zarr, just now with modality-specific obs/var/X/etc like mod/{modality}/obs/colname

We can then build on this feature and add modality-specific file types and components, such as a chromatin accessibility peak count matrix for a MuData object with mod/atac/X

Checklist

• Ensure PR works with all demos on the dev.vitessce.io homepage
• Open (draft) PR's into vitessce-python and vitessce-r if this is a release PR
• Documentation added or updated