Support for external entities

[Pierstoval]

Goal:

• Be able to load an entity from an external Crud configuration
• Configure the loading process via StateProvider options
• Customize the fields that will be displayed (with real Field instances coming from the external crud)
• Create detailed forms with a list of external entities, with hardcoded filters (dynamic filters are a bit too complex for now)

[Pierstoval]

Current state if the Test crud config has a relation with the Book crud:

Field config in "list" operation:

new CrudEntityField('crud_entity_field', 'Crud entity field (book)', {
	crud_name: 'books',
	get_provider_operation: {
		entity_field: 'title',
	},
})