Allow saving OME-NGFF metadata in-place

[andy-sweet]

The Save button currently exists, but is always disabled.

The intent is for this button to save the layer's metadata in-place. In general, the layer might not be backed by a file and even if it is we probably won't know what file(s) to change to update the metadata appropriately.

Therefore, this issue is focused on supporting in-place saving layers that are backed by OME-NGFF zarr directories that we have write access too. We may want to restrict this further to layers that were loaded with this plugin, since it may be easier to keep track of the file to overwrite then.

If the currently selected layer does not support saving in-place, then the button should be disabled ideally with a tooltip to explain why.