Allow 'Reference' field to be programmatically added when extending the admin area

[chanesteves]

Is your feature request related to a problem? Please describe.

Not a problem, just a new feature request 🎉

I used yarn webiny scaffold to extend the admin area and it allowed me to create a screens/pages that perform CRUD operations using a form. Unfortunately, @webiny/ui library just allowed me to add simple text, select and autocomplete fields into the form. I wish I could programmatically add Reference field into the extended admin area's form.

Describe the feature's behavior.

Ideally, the Reference field would work in the extended admin area's page the same way it works in Headless CMS Content Model. With this field, we should be able to reference the content models under Headless CMS as well as the models created by extending the admin area.

Ideally, too, all the following field types in Headless CMS Content Model can be programmatically added but the Reference field is a good start.

Describe alternatives you've considered.

For now, I've used the Autocomplete field as an alternative.

[chanesteves]

Hello, just following up for any updates in this issue.