Dispatch fdsnws-station POST requests

[damb]

Evidently, the current Compose deployment of eidaws-federator does not correctly dispatch fdsnws-station HTTP POST requests. That is, if the request message body looks e.g.

level=network
format=text

CH * * * 2019-01-01 2019-01-02

the service returns with HTTP status code 400 including an error message such as e.g.

Error 400: Bad request

{'format': ['Must be one of: xml.']}

Usage details are available from http://www.fdsn.org/webservices/

Request:
http://localhost:8080/eidaws/station/xml/1/query

Request Submitted:
2021-04-08T09:51:21.919707

Service version:
0.11.8

This is because the Frontend Reverse Proxy does not analyze the request message body, and thus dispatches by default to a fdsnws-station-xml backend service. As a consequence, this issue can only be fixed if the Frontend Reverse Proxy parses the request message body in order to correctly detect the response format requested.