Host indentification for RBG Service

RBG service is common for Public and DEI. Hence, a x-filespin-saas-host sent by caller is used by RBG to identify the SaaS host.

When a RBG call is received at SaaS endpoint, SaaS adds its host automatically (via nginx lua script) and forwards it

When a RBG call is received directly to rbg service (rbg-addon.filespin.io), RBG expects this header x-filespin-saas-host to be sent with the correct host.