docs: add some clarification around the use of metadata in ExtAuthZ (#30563)

Signed-off-by: Rohit Agrawal <rohit.agrawal@databricks.com>
Co-authored-by: phlax <phlax@users.noreply.github.com>

Mirrored from https://github.com/envoyproxy/envoy @ 8f804787815a17debce1222a7b65ff67418475f9

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

@@ -91,7 +91,10 @@ message ExtAuthz {
   type.v3.HttpStatus status_on_error = 7;
 
   // Specifies a list of metadata namespaces whose values, if present, will be passed to the
-  // ext_authz service. :ref:`filter_metadata <envoy_v3_api_field_config.core.v3.Metadata.filter_metadata>` is passed as an opaque ``protobuf::Struct``.
+  // ext_authz service. The :ref:`filter_metadata <envoy_v3_api_field_config.core.v3.Metadata.filter_metadata>`
+  // is passed as an opaque ``protobuf::Struct``.
+  //
+  // Please note that this field exclusively applies to the gRPC ext_authz service and has no effect on the HTTP service.
   //
   // For example, if the ``jwt_authn`` filter is used and :ref:`payload_in_metadata
   // <envoy_v3_api_field_extensions.filters.http.jwt_authn.v3.JwtProvider.payload_in_metadata>` is set,
@@ -105,10 +108,13 @@ message ExtAuthz {
   repeated string metadata_context_namespaces = 8;
 
   // Specifies a list of metadata namespaces whose values, if present, will be passed to the
-  // ext_authz service. :ref:`typed_filter_metadata <envoy_v3_api_field_config.core.v3.Metadata.typed_filter_metadata>` is passed as an ``protobuf::Any``.
+  // ext_authz service. :ref:`typed_filter_metadata <envoy_v3_api_field_config.core.v3.Metadata.typed_filter_metadata>`
+  // is passed as a ``protobuf::Any``.
+  //
+  // Please note that this field exclusively applies to the gRPC ext_authz service and has no effect on the HTTP service.
   //
-  // It works in a way similar to ``metadata_context_namespaces`` but allows envoy and external authz server to share the protobuf message definition
-  // in order to do a safe parsing.
+  // It works in a way similar to ``metadata_context_namespaces`` but allows Envoy and ext_authz server to share
+  // the protobuf message definition in order to do a safe parsing.
   //
   repeated string typed_metadata_context_namespaces = 16;