[Add forge now] Fix support of browsers with Javascript disabled

When filling the form at http://127.0.0.1:5004/add-forge/request/create in a browser with Javascript disabled, the form is successfully processed by the server, but it errors while trying to render the response:

 Error
500
Internal Server Error

ImproperlyConfigured: Returned a template response with no `template_name` attribute set on either the view or response

!1073 (closed)

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Migrated from T4053 (view on Phabricator)