Allow Custom "Empty State" Message for Relationship Fields in Admin UI

[muslewski]

Currently, when using a relationship field in the Payload admin UI, if there are no available items to select, the field displays a default "No options" message. This is functional, but in many use cases—especially when the available options are filtered dynamically—it would be much more user-friendly to allow admins to customize this empty state message.

Feature request:
Add support for a property (e.g., admin.emptyStateMessage) on relationship fields, so that when no options are available, a custom message can be shown instead of the default "No options". This would allow us to provide editors with helpful instructions, such as:

"Select at least one related item in order to see it here."

Use case:
For example, if a relationship field is filtered to only show items that reference the current document, and none exist yet, the admin could display:

"Add this service to at least one project to see it here."

This small feature would improve the editorial experience and reduce confusion for content editors. Thank you for considering!