local_ratelimit: allow sharing token bucket between filter chains (#20340)

Signed-off-by: Greg Greenway <ggreenway@apple.com>

Mirrored from https://github.com/envoyproxy/envoy @ 5f8860ba5dbc96942de09b33bf8701e2046c9035

envoy/extensions/filters/network/local_ratelimit/v3/local_rate_limit.proto

@@ -33,7 +33,8 @@ message LocalRateLimit {
   // the connection will be immediately closed.
   //
   // .. note::
-  //   In the current implementation each filter and filter chain has an independent rate limit.
+  //   In the current implementation each filter and filter chain has an independent rate limit, unless
+  //   a shared rate limit is configured via :ref:`share_key <envoy_v3_api_field_extensions.filters.network.local_ratelimit.v3.LocalRateLimit.share_key>`.
   //
   // .. note::
   //   In the current implementation the token bucket's :ref:`fill_interval
@@ -44,4 +45,10 @@ message LocalRateLimit {
   // Runtime flag that controls whether the filter is enabled or not. If not specified, defaults
   // to enabled.
   config.core.v3.RuntimeFeatureFlag runtime_enabled = 3;
+
+  // Specifies that the token bucket used for rate limiting should be shared with other local_rate_limit filters
+  // with a matching :ref:`token_bucket <envoy_v3_api_field_extensions.filters.network.local_ratelimit.v3.LocalRateLimit.token_bucket>`
+  // and `share_key` configuration. All fields of `token_bucket` must match exactly for the token bucket to be shared. If this
+  // field is empty, this filter will not share a token bucket with any other filter.
+  string share_key = 4;
 }