During file uploads, Workhorse will set a JWT param per file upload that
contain all the upload params.
`multipart.rb` has been modified to support these params so
that `UploadedFile`s are built from those signed params.

This behavior change is gated behind a feature flag:
:upload_middleware_jwt_params_handler

Support the changes done in:
https://gitlab.com/gitlab-org/gitlab-workhorse/-/merge_requests/490