Compact UI submit button is slow and does not disable itself on click, making it possible to create duplicate media

Problem/Motivation

It is easy for editors to accidentally create duplicate media entities using the Bynder compact UI. The "Add asset" button is slow to respond and does not disable itself when the user clicks, so editors can be confused into thinking they need to click it again, while things are working in the background. This results in multiple Bynder entities being created for the same asset.

GIF screencast showing issue

Steps to reproduce

Select an asset with the Compact UI, click the "Add asset" button, confirm the button shows an ajax load, but then goes back to "Add asset" and is clickable again before the browser submits.

Proposed resolution

Disable the "Add asset" button until the form is complete.

Remaining tasks

User interface changes

API changes

None expected

Data model changes

None expected