ratelimit support stat prefix (#30677)

Risk Level: low
Testing: ut

Signed-off-by: wangkai19 <wangkai19@corp.netease.com>

Mirrored from https://github.com/envoyproxy/envoy @ a33cde6cea0cf4bfb700a9002175e74553dc52a4

envoy/extensions/filters/http/ratelimit/v3/rate_limit.proto

@@ -25,7 +25,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // Rate limit :ref:`configuration overview <config_http_filters_rate_limit>`.
 // [#extension: envoy.filters.http.ratelimit]
 
-// [#next-free-field: 13]
+// [#next-free-field: 14]
 message RateLimit {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.filter.http.rate_limit.v2.RateLimit";
@@ -130,6 +130,10 @@ message RateLimit {
   // Sets the HTTP status that is returned to the client when the ratelimit server returns an error
   // or cannot be reached. The default status is 500.
   type.v3.HttpStatus status_on_error = 12;
+
+  // Optional additional prefix to use when emitting statistics. This allows to distinguish
+  // emitted statistics between configured ``ratelimit`` filters in an HTTP filter chain.
+  string stat_prefix = 13;
 }
 
 // Global rate limiting :ref:`architecture overview <arch_overview_global_rate_limit>`.