docs: Add a warning about undocumented behavioral changes when excluding stats (#9883)

Signed-off-by: Doug Jones <djones@squarespace.com>

Mirrored from https://github.com/envoyproxy/envoy @ 0daadad1d70faa222d941c439c232e6d01a58ca8

envoy/config/metrics/v2/stats.proto

@@ -67,6 +67,11 @@ message StatsConfig {
   // Inclusion/exclusion matcher for stat name creation. If not provided, all stats are instantiated
   // as normal. Preventing the instantiation of certain families of stats can improve memory
   // performance for Envoys running especially large configs.
+  //
+  // .. warning::
+  //   Excluding stats may affect Envoy's behavior in undocumented ways. See
+  //   `issue #8771 <https://github.com/envoyproxy/envoy/issues/8771>`_ for more information.
+  //   If any unexpected behavior changes are observed, please open a new issue immediately.
   StatsMatcher stats_matcher = 3;
 }
 

envoy/config/metrics/v3/stats.proto

@@ -76,6 +76,11 @@ message StatsConfig {
   // Inclusion/exclusion matcher for stat name creation. If not provided, all stats are instantiated
   // as normal. Preventing the instantiation of certain families of stats can improve memory
   // performance for Envoys running especially large configs.
+  //
+  // .. warning::
+  //   Excluding stats may affect Envoy's behavior in undocumented ways. See
+  //   `issue #8771 <https://github.com/envoyproxy/envoy/issues/8771>`_ for more information.
+  //   If any unexpected behavior changes are observed, please open a new issue immediately.
   StatsMatcher stats_matcher = 3;
 }