buffer filter: Deprecate `max_request_time` timeout (#5290)

Description: The new request_timeout in http connection manager covers the filter chain.
Risk Level: N/A
Fixes #4830
Signed-off-by: Auni Ahsan <auni@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 92e932a9a26ca178ad77a8e3616fadd57d3f807d

envoy/config/filter/http/buffer/v2/buffer.proto

@@ -19,13 +19,10 @@ message Buffer {
 
   // The maximum number of seconds that the filter will wait for a complete
   // request before returning a 408 response.
-  google.protobuf.Duration max_request_time = 2 [
-    (validate.rules).duration = {
-      required: true,
-      gt: {}
-    },
-    (gogoproto.stdduration) = true
-  ];
+  // deprecated in favor of http connection manager of :ref:request timeouts
+  // <envoy_api_field_config.filter.network.http_connection_manager.v2.HttpConnectionManager.request_timeout>
+  google.protobuf.Duration max_request_time = 2
+      [deprecated = true, (validate.rules).duration = {gt: {}}, (gogoproto.stdduration) = true];
 }
 
 message BufferPerRoute {