Requests are not properly proxied to pyff

[llndqvst]

Requests are not properly proxied to pyff.

With thiss-js running in a container built from thiss-js/staging with pyff running curl -LI http://localhost:8080/entities/undefined.json returns

HTTP/1.1 404 Not Found
Server: nginx/1.10.3
Date: Fri, 17 Jun 2022 06:15:53 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 169
Connection: keep-alive

With proxying properly configured the same request returns

HTTP/1.1 200 OK
Server: nginx/1.10.3
Date: Fri, 17 Jun 2022 06:21:30 GMT
Content-Type: application/json; charset=utf-8
Content-Length: 2
Connection: keep-alive
ETag: 97d170e1550eee4afc0af065b78cda302a97674c
Expires: Fri, 17 Jun 2022 08:21:30 GMT
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: POST,GET,DELETE,PUT,OPTIONS
Access-Control-Allow-Headers: Origin, Content-Type, Accept, Authorization
Access-Control-Allow-Credentials: true
Access-Control-Max-Age: 1728000

This is fixed by #233