dfp: add support for DFP honoring dynamic_host filter state when configured (#39605)

Signed-off-by: Rohit Agrawal <rohit.agrawal@databricks.com>
Co-authored-by: yanavlasov <yavlasov@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 877b9824370232745db11cf65417b8d88b4d38c5

Author: update-envoy[bot]

envoy/extensions/filters/http/dynamic_forward_proxy/v3/dynamic_forward_proxy.proto

@@ -41,6 +41,17 @@ message FilterConfig {
   // ``envoy.stream.upstream_address`` (See
   // :repo:`upstream_address.h<source/common/stream_info/upstream_address.h>`).
   bool save_upstream_address = 2;
+
+  // When this flag is set, the filter will check for the ``envoy.upstream.dynamic_host``
+  // and/or ``envoy.upstream.dynamic_port`` filter state values before using the HTTP
+  // Host header for DNS resolution. This provides consistency with the
+  // :ref:`SNI dynamic forward proxy <envoy_v3_api_msg_extensions.filters.network.sni_dynamic_forward_proxy.v3.FilterConfig>` and
+  // :ref:`UDP dynamic forward proxy <envoy_v3_api_msg_extensions.filters.udp.udp_proxy.session.dynamic_forward_proxy.v3.FilterConfig>`
+  // filters behavior when enabled.
+  //
+  // If the flag is not set (default), the filter will use the HTTP Host header
+  // for DNS resolution, maintaining backward compatibility.
+  bool allow_dynamic_host_from_filter_state = 4;
 }
 
 // Per route Configuration for the dynamic forward proxy HTTP filter.