Add dynamic content to autocomplete/dropdown lists

### Describe the feature you'd like to request

It would be nice if Amplify had the ability to get dropdown list values dynamically from a table, as I imagine this is a feature others would use as well.

### Describe your use case and how the feature would improve your experience.

My client wants to be able to have users enter new values into an autocomplete form, which are not existing options. They want to be able to have an admin approve new values which get added to the dropdown list.

### Describe alternatives you've considered

I have considered either using a build script to get the values from the table and add them into the page before deploying the static content.

To update the values dynamically, I think I can figure out a way to have the frontend query an API which checks the 'approved values per field' table and updates the dropdown list in the frontend, but manually editing bundled js components is going to be a pain.
it would be nice if this was a built-in feature.

### Additional context

related amplify js [issue](https://github.com/aws-amplify/amplify-js/issues/13402)

Start by reviewing the related Amplify JS issue and the existing autocomplete/dropdown entry points; this issue names no files or tests. Clarify the design for loading table-backed values, user-submitted values, and admin approval before implementation, then define completion around dynamically updating approved dropdown options without editing bundled JavaScript.

Written by the indexing model from the issue text.