Disable sorting on many relationships

[timleslie]

Sorting a list by a many relationship doesn't have a meaningful interpretation. In practice, attempting to do this would return errors. This change prevents the Admin UI from throwing errors from the list view when a user attempts to sort by a man relationship.

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🦋 Changeset detected

Latest commit: 95baee0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@keystone-next/app-basic	Patch
@keystone-next/example-todo	Patch
@keystone-next/fields	Patch

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[gwyneplaine]

lgtm