Add server_domain field in questions requests to Robotoff

[raphael0202]

We want Robotoff insights to be specific to each website (off, off-pro, openbeautyfacts, openpetfoodfacts, openproductfacts) and to each environment (dev, prod).
This has been taken care of on Robotoff side (see openfoodfacts/robotoff#47), we now need to only display insights that match the server domain (website + environment).
A server_domain field is currently sent to the /api/v1/webhook/product endpoint. We also need to send this field when requesting new Robotoff questions on /api/v1/questions/{barcode}. See the API documentation for more information.

Known values for the server_domain field (according what robotoff webhook endpoint receives):

api.pro.openfoodfacts.org
api.openfoodfacts.org
api.openfoodfacts.net
api.pro.openfoodfacts.dev

For completeness, here is the issue that added Robotoff webhook ping: #1707.