[envoy/admin] Scaffolding for structured admin and config_dump endpoint (#532)

See envoyproxy/envoy#2771 for context

I will add documentation once the interfaces and placement of these things is settled. Current location (new admin package) was agreed upon as a good start with @htuch but i don't feel strongly about that or naming.

Signed-off-by: James Sedgwick <jsedgwick@lyft.com>

envoy/admin/v2/BUILD

@@ -0,0 +1,12 @@
+load("//bazel:api_build_system.bzl", "api_proto_library")
+
+licenses(["notice"])  # Apache 2
+
+api_proto_library(
+    name = "config_dump",
+    srcs = ["config_dump.proto"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//envoy/api/v2:rds",
+    ],
+)

envoy/admin/v2/config_dump.proto

@@ -0,0 +1,35 @@
+syntax = "proto3";
+
+package envoy.admin.v2;
+
+import "google/protobuf/any.proto";
+import "envoy/api/v2/rds.proto";
+
+import "gogoproto/gogo.proto";
+
+// [#protodoc-title: ConfigDump]
+// [#proto-status: draft]
+
+// The /config_dump admin endpoint uses this wrapper message to maintain and serve arbitrary
+// configuration information from any component in Envoy.
+// TODO(jsedgwick) In the future, we may want to formalize this further with an RPC for config_dump,
+// and perhaps even with an RPC per config type. That strategy across all endpoints will allow for
+// more flexibility w.r.t. protocol, serialization, parameters, etc.
+message ConfigDump {
+  // This map is serialized and dumped in its entirety at the /config_dump endpoint.
+  //
+  // Keys should be a short descriptor of the config object they map to. For example, envoy's HTTP
+  // routing subsystem might use "routes" as the key for its config, for which it uses the message
+  // RouteConfigDump as defined below. In the future, the key will also be used to filter the output
+  // of the /config_dump endpoint.
+  map<string, google.protobuf.Any> configs = 1 [(gogoproto.nullable) = false];
+}
+
+// Envoy's RDS implementation fills this message with all currently loaded routes, as described by
+// their RouteConnfiguration objects. Static routes configured in the bootstrap configuration are
+// separated from those configured dynamically via RDS. This message is available at the
+// /config_dump admin endpoint.
+message RouteConfigDump {
+  repeated envoy.api.v2.RouteConfiguration static_route_configs = 1 [(gogoproto.nullable) = false];
+  repeated envoy.api.v2.RouteConfiguration dynamic_route_configs = 2 [(gogoproto.nullable) = false];
+}

envoy/api/v2/BUILD

@@ -8,6 +8,7 @@ licenses(["notice"])  # Apache 2
 package_group(
     name = "friends",
     packages = [
+        "//envoy/admin/...",
         "//envoy/api/v2",
         "//envoy/config/...",
         "//envoy/service/...",