hot restart: provide a mechanism for obtaining a base-id dynamically (#11357)

Provides a --use-dynamic-base-id flag to select an unused base-id.
Primarily useful for testing, but generally available. Adds a
--base-id-path flag where Envoy writes the base id to a file.
Converts tests to use the dynamic base id selection rather than
trying to keep all base ids unique.

Signed-off-by: Stephan Zuercher <zuercher@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 69f2dfcae15401f14d7cc3c829fd32ff2efc9f0c

envoy/admin/v3/server_info.proto

@@ -54,7 +54,7 @@ message ServerInfo {
   CommandLineOptions command_line_options = 6;
 }
 
-// [#next-free-field: 31]
+// [#next-free-field: 33]
 message CommandLineOptions {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.admin.v2alpha.CommandLineOptions";
@@ -82,6 +82,12 @@ message CommandLineOptions {
   // See :option:`--base-id` for details.
   uint64 base_id = 1;
 
+  // See :option:`--use-dynamic-base-id` for details.
+  bool use_dynamic_base_id = 31;
+
+  // See :option:`--base-id-path` for details.
+  string base_id_path = 32;
+
   // See :option:`--concurrency` for details.
   uint32 concurrency = 2;
 

envoy/admin/v4alpha/server_info.proto

@@ -54,7 +54,7 @@ message ServerInfo {
   CommandLineOptions command_line_options = 6;
 }
 
-// [#next-free-field: 31]
+// [#next-free-field: 33]
 message CommandLineOptions {
   option (udpa.annotations.versioning).previous_message_type = "envoy.admin.v3.CommandLineOptions";
 
@@ -81,6 +81,12 @@ message CommandLineOptions {
   // See :option:`--base-id` for details.
   uint64 base_id = 1;
 
+  // See :option:`--use-dynamic-base-id` for details.
+  bool use_dynamic_base_id = 31;
+
+  // See :option:`--base-id-path` for details.
+  string base_id_path = 32;
+
   // See :option:`--concurrency` for details.
   uint32 concurrency = 2;