Remove unnecessary XDN header when sending request to container

[fadhilkurnia]

Currently, XDN uses the XDN header in the HTTP requests to determine the service name.
However, XDN does not remove that header before forwarding that message to the container, even though that header is commonly meaningless for the containerized application.
Having that header for XDN <=> Container reduces the performance because
(1) that header is also sent to the Container, and
(2) that header stays in the request being agreed upon by Paxos.

Needed changes

• Remove the XDN header once the HTTP request is received by XdnHttpActiveReplica.
• Specifically, having the serviceName field in XdnHttpRequest.
• Update protobuf format of XdnHttpRequest to store the service name in a dedicated field, instead of embedding it inside the header. This will not add much performance, but we are reducing ~3 bytes of overhead (i.e., because of XDN in the header).