Add set_filter_state HTTP filter support

[Eeshu-Yadav]

This adds full support for theset_filter_state HTTP filter in Orion.it parses Envoy / Istio set_filter_stateconfigs, evaluates substitution format strings (e.g. %REQ(:authority)%, %DOWNSTREAM_REMOTE_ADDRESS%), and stores the resulting values in a thread-safe runtime FilterState with metadata (read-only, shared-with-upstream). This enables Istio waypoint use-cases where the CONNECT :authority and client address must be extracted and propagated for routing and policy decisions.