Add `MetadataOnly` to `METADATA.ome.xml`?

[melissalinkert]

Discussed briefly in formats meeting (/cc @joshmoore, @sbesson, @dgault).

METADATA.ome.xml doesn't technically validate, because it doesn't have MetadataOnly, BinData, or TiffData under Pixels. This was sort of intentional, as adding a MetadataOnly here means that raw2ometiff then needs to remove it. Since we're now using the output of bioformats2raw independent of raw2ometiff and suggesting that other applications could use METADATA.ome.xml, it probably makes sense to update this.

[joshmoore]

btw, apparently when there are plane elements this gets even trickier: ome/ome-zarr-metadata@08e12f7#diff-0bb17e0ecb4ac83835ee3800a1af71a12f644b0ce782c623ba97f8917916250eR54

[sbesson]

Is the Plane validation issue related to ome/bioformats#3810 ? In this case, I think the issue came from ome_types rather than a core invalidity

[joshmoore]

Almost certainly.