Upload designs through modal with commit message

Problem to solve

Uploading designs doesn't give you an opportunity to add a commit message. The current flow is:

1. Click "Add designs"
2. Select designs to upload
3. Click "Upload"

Intended users

Users who add designs.

Further details

Proposal

Add an upload modal (similar to the upload file modal) where you can add your designs and commit message. This modal potentially adds the ability to have thumbnail previews as well.

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

What is the type of buyer?

Links / references

cc @phikai