Request for adding new items to models: drop-down selections for arrays

**Is your feature request related to a problem? Please describe.**
When using the content management form for adding new items to a model, there does not currently seem to be any way of displaying a pre-defined set of options for certain fields.

For example, if I'm adding multiple items to an array within a model, I need to manually type each possible array item into the field for every item in that particular table model. This process can be needlessly cumbersome and error prone, as I may mistype an array item and/or forgot to include certain items from the list.

**Describe the solution you'd like**
I would love to have the ability within Admin UI to create a pre-defined drop down list that I can multi-select from in order to populate array data within a model table.

**Describe alternatives you've considered**
The only two alternatives that I can think of are:

1) Modifying my GraphQL schema so that arrays are instead divided into boolean properties. This would involve creating a boolean for each possible selection from the given list of items, rather than starting each model item with an empty array for these properties. Having the ability to click on the true/false switch provided by the Admin UI form might be easier than having to refer to a list of all possible items to include in an array.

The problem with this solution, however, is that it would create a very messy-looking data model, as there could be a very large list of boolean values to choose from for certain models that I'm currently working with. Arrays simply make more logical sense for most of these.

2) Creating my own forms to work with the API endpoints for these models. I could manually add drop-down lists to populate array fields.

The perhaps obvious downside to this solution is that it involves creating an entire UI form from scratch. This is a lot of extra work considering the only person who will likely have access to these API mutations will be myself (and maybe someone to whom I grant admin access). General users of my app will not be adding or editing these data models.

**Additional context**
Here is an example screenshot, featuring one of the Admin UI forms that I'm referring to. Note the arrays for "allergies," "diets," etc. I had to type those in manually, but it would be very helpful to be able to quickly select those from a list.


The issue names no files, tests, or entry points. Start by locating the Admin UI form component that edits array fields and how GraphQL schema metadata reaches it; done means array fields can present predefined options with multi-select behavior in the admin form.

Written by the indexing model from the issue text.