support uploading files with JWT

[MegaphoneJon]

Overview

If you access a FormBuilder form with a "secret link" (JWT), you can't upload files, even if you ordinarily have the permission to do so.

Before

403 error on Afform.submitFiles.

After

File successfully uploads.

Technical Details

There are two issues:

• the JWT is normally only passed via jQuery.ajaxSetup(), which doesn't persist if that function is called again. So we explicitly set the header when sending the file.
• The POST request format for files is different, so values that might ordinarily be in values are at the top level of the POST submission. So we must allow them in allowFields.

[civibot]

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[mattwire]

@MegaphoneJon Just to confirm is the form in "Form based" permissions mode?

[MegaphoneJon]

@mattwire Yes.