dns: adding limits to the key value store. (#20698)

Risk Level: low
Testing: unit tests
Docs Changes: inline
Release Notes:
[Optional Runtime guard:]

Signed-off-by: Alyssa Wilk <alyssar@chromium.org>

Mirrored from https://github.com/envoyproxy/envoy @ 888c60386039e05da5a5c1f30fda625b4cbe13a8

envoy/extensions/key_value/file_based/v3/config.proto

@@ -3,6 +3,7 @@ syntax = "proto3";
 package envoy.extensions.key_value.file_based.v3;
 
 import "google/protobuf/duration.proto";
+import "google/protobuf/wrappers.proto";
 
 import "xds/annotations/v3/status.proto";
 
@@ -28,4 +29,8 @@ message FileBasedKeyValueStoreConfig {
 
   // The interval at which the key value store should be flushed to the file.
   google.protobuf.Duration flush_interval = 2;
+
+  // The maximum number of entries to cache, or 0 to allow for unlimited entries.
+  // Defaults to 1000 if not present.
+  google.protobuf.UInt32Value max_entries = 3;
 }