[LH Doc Upload] Veteran-uploaded docs (bugfix) filename error

[ajones446]

Nathan caught this during manual testing on staging.

When submitting an upload, an error message returned "no filename" for this line

upload_document = provider.generate_upload_document(attachment.converted_filename)

It should fall back to the upload data "name" key as is done here with the existing: https://github.com/department-of-veterans-affairs/vets-api/blob/master/app/sidekiq/evss/disability_compensation_form/submit_uploads.rb#L162