async grpc: make grpc client eviction time configurable (#30708)

Make the cached grpc client eviction time configurable, and before it is fixed 50s.

Risk Level: Low
Testing:
Docs Changes:
Release Notes:
Platform Specific Features:

Signed-off-by: Boteng Yao <boteng@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 83c66e18e7a32c77cf084dc8bb797c84a3e84bec

envoy/config/bootstrap/v3/bootstrap.proto

@@ -41,7 +41,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // <config_overview_bootstrap>` for more detail.
 
 // Bootstrap :ref:`configuration overview <config_overview_bootstrap>`.
-// [#next-free-field: 40]
+// [#next-free-field: 41]
 message Bootstrap {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.bootstrap.v2.Bootstrap";
@@ -136,6 +136,13 @@ message Bootstrap {
     bool enable_deferred_creation_stats = 1;
   }
 
+  message GrpcAsyncClientManagerConfig {
+    // Optional field to set the expiration time for the cached gRPC client object.
+    // The minimal value is 5s and the default is 50s.
+    google.protobuf.Duration max_cached_entry_idle_duration = 1
+        [(validate.rules).duration = {gte {seconds: 5}}];
+  }
+
   reserved 10, 11;
 
   reserved "runtime";
@@ -401,6 +408,9 @@ message Bootstrap {
 
   // Optional application log configuration.
   ApplicationLogConfig application_log_config = 38;
+
+  // Optional gRPC async manager config.
+  GrpcAsyncClientManagerConfig grpc_async_client_manager_config = 40;
 }
 
 // Administration interface :ref:`operations documentation