Each Undertow server should expose a distinct SessionIdentifierCodec

Undertow exposes a single instance-id for the whole subsystem. This id is used by a load balancer to uniquely identify the node among other nodes in the load balancing group. However, this granularity is not correct.

Undertow can define multiple servers, each with a unique set of listeners. From the perspective of the load balancer, these servers are distinct and thus must use distinct names. Thus, rather than installing a single SessionIdentifierCodec for the subsystem, we should install one instance per server.