udp_session_filters: add API for session filters and apply in UDP proxy (#29366)

Signed-off-by: ohadvano <ohadvano@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 83a7d934cdb98ca8779a9c72795ef2da0345f61c

envoy/extensions/filters/udp/udp_proxy/v3/udp_proxy.proto

@@ -5,6 +5,7 @@ package envoy.extensions.filters.udp.udp_proxy.v3;
 import "envoy/config/accesslog/v3/accesslog.proto";
 import "envoy/config/core/v3/udp_socket_config.proto";
 
+import "google/protobuf/any.proto";
 import "google/protobuf/duration.proto";
 
 import "xds/annotations/v3/status.proto";
@@ -26,7 +27,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // [#extension: envoy.filters.udp_listener.udp_proxy]
 
 // Configuration for the UDP proxy filter.
-// [#next-free-field: 11]
+// [#next-free-field: 12]
 message UdpProxyConfig {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.filter.udp.udp_proxy.v2alpha.UdpProxyConfig";
@@ -49,6 +50,18 @@ message UdpProxyConfig {
     }
   }
 
+  // Configuration for UDP session filters.
+  message SessionFilter {
+    // The name of the filter configuration.
+    string name = 1 [(validate.rules).string = {min_len: 1}];
+
+    oneof config_type {
+      // Filter specific configuration which depends on the filter being
+      // instantiated. See the supported filters for further documentation.
+      google.protobuf.Any typed_config = 2;
+    }
+  }
+
   // The stat prefix used when emitting UDP proxy filter stats.
   string stat_prefix = 1 [(validate.rules).string = {min_len: 1}];
 
@@ -110,4 +123,7 @@ message UdpProxyConfig {
 
   // Configuration for proxy access logs emitted by the UDP proxy. Note that certain UDP specific data is emitted as :ref:`Dynamic Metadata <config_access_log_format_dynamic_metadata>`.
   repeated config.accesslog.v3.AccessLog proxy_access_log = 10;
+
+  // Optional session filters that will run for each UDP session.
+  repeated SessionFilter session_filters = 11;
 }