Documentation about the media type

[m-mohr]

I'm not sure this is the right repository, please move it if there's a better place.

The media type for ZARR is not properly documented imho. I think we should clarify:

• What the base media type is (i.e. application/vnd.zarr, see also Base media type incorrect data-pipeline#97)
• Which ZARR versions are supported (only v2? see also wrong mime-type reporting Zarr V2 instead of v3 data-pipeline#95)
• Which values are allowed for profile (only multiscales? If multiple values are allowed at the same time, how to provide them? comma separated?)