DEV: Bump Uppy to v2.X and rebuild bundle (#14173)

Uppy V2 includes the S3 multipart batch presigning change
we contributed in d613b849a6
so we need to upgrade it. This also brings both package.json
files into line and accounts for the renaming of Plugin
to BasePlugin in Uppy.

This has been tested and is working locally for both
regular Ember and Ember CLI, for uploads.json
XHR uploads and for direct S3 uploads (single and multipart).

vendor/assets/javascripts/custom-uppy.js

@@ -5,7 +5,6 @@
 // use the plugins we actually want.
 window.Uppy = {}
 Uppy.Core = require('@uppy/core')
-Uppy.Plugin = Uppy.Core.Plugin
 Uppy.XHRUpload = require('@uppy/xhr-upload')
 Uppy.AwsS3 = require('@uppy/aws-s3')
 Uppy.AwsS3Multipart = require('@uppy/aws-s3-multipart')