Is your feature request related to a problem? Please describe.
File uploads management should be handled by a dedicated tool, to bring good features and more resiliency.
Uppy seems appropriate as it is made to be integrated and is well maintained.

Describe the solution you'd like
As described in #2243, using a dedicated library to manage uploads would solve a bunch of main issues about file or images upload.
I think Uppy is a better candidate than Filepond, as its code is already divided in modules, so we could easily use @uppy/core with Netlify CMS UI.

Additional context
You can find screenshots and documentation on the Uppy website.