Dynamic Modules Added Envoy Dynamic Module Callback

Added envoy_dynamic_module_callback_cluster_lb_context_get_filter_state_bytes and envoy_dynamic_module_callback_cluster_lb_context_get_filter_state_typed ABI callbacks so that a dynamic-module cluster's load balancer can read filter state set by an upstream HTTP filter (or any other producer) when picking a host. The Rust SDK exposes these as ClusterLbContext::get_filter_state_bytes and ClusterLbContext::get_filter_state_typed.