Working on RelationshipFilter Enhancements

[epicmau5time]

I was considering adding the ability for a basic multiselect for the relationship filter select dropdown, without needing the field itself to have {hasMany: true} flagged. I am still working to see if it can be done for when multiple relationships are supplied {relationTo: [...]} but I wanted to know if there was a specific reason this was left out in the past before I continue and it gets shot down.

I am also testing the ability to have the dropdown remain open if the list has more than one option and isMulti is enabled so users can select more than one option without needing to reopen the dropdown on each selection.

Would these be useful additions?