mobile: making api listener configurable (#24745)

Adding envoy.reloadable_features.use_api_listener to control if the regular listener manager or the api listener manager is used. note this does not use the usual reloadable or restart flags mechanism (due to it not being loaded at the time) but instead checks for the string literal in bootstrap YAML.

Risk Level: low
Testing: new integration test
Docs Changes: n/a
Release Notes: n/a

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

Mirrored from https://github.com/envoyproxy/envoy @ a9d852b50511c1ff59a96815a38811f9853b00ed

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: 37]
+// [#next-free-field: 38]
 message Bootstrap {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.bootstrap.v2.Bootstrap";
@@ -354,6 +354,12 @@ message Bootstrap {
   //    See :repo:`xds_config_tracker_integration_test <test/integration/xds_config_tracker_integration_test.cc>`
   //    for an example usage of the interface.
   core.v3.TypedExtensionConfig xds_config_tracker_extension = 36;
+
+  // [#not-implemented-hide:]
+  // This controls the type of listener manager configured for Envoy. Currently
+  // Envoy only supports ListenerManager for this field and Envoy Mobile
+  // supports ApiListenerManager.
+  core.v3.TypedExtensionConfig listener_manager = 37;
 }
 
 // Administration interface :ref:`operations documentation

envoy/config/listener/v3/listener.proto

@@ -372,3 +372,15 @@ message Listener {
   // :ref:`global_downstream_max_connections <config_overload_manager_limiting_connections>`.
   bool ignore_global_conn_limit = 31;
 }
+
+// A placeholder proto so that users can explicitly configure the standard
+// Listener Manager via the bootstrap's :ref:`listener_manager <envoy_v3_api_field_config.bootstrap.v3.Bootstrap.listener_manager>`.
+// [#not-implemented-hide:]
+message ListenerManager {
+}
+
+// A placeholder proto so that users can explicitly configure the API
+// Listener Manager via the bootstrap's :ref:`listener_manager <envoy_v3_api_field_config.bootstrap.v3.Bootstrap.listener_manager>`.
+// [#not-implemented-hide:]
+message ApiListenerManager {
+}