Payload v3 accepts only single file uploads, export fetchAPIFileUpload as a workaround

Describe the Bug

Payload v2 used to be able to handle any shape of multipart data and parse files accordingly. v3 is only able to find a single file named file.

Ideally as a long term solution it would be great to have payload automatically figure out data types passed in a multipart body and create matching data structure. So just req.files = files and done I guess...

As a quick and dirty fix it would be also great to just expose fetchAPIFileUpload so that end users can easily create custom body parsers while still using global payload upload configuration.

Link to the code that reproduces this issue

https://github.com/payloadcms/payload/blob/main/packages/next/src/fetchAPI-multipart/index.ts

Reproduction Steps

upgrade to v3
make sad noises attempting to migrate file uploads

Which area(s) are affected? (Select all that apply)

area: core

Environment Info

v3