tracing: Add support for sending data in Zipkin v2 format (#6985)

Description: This patch supports sending a list of spans as JSON v2 and protobuf message over HTTP to Zipkin collector. [Sending protobuf](https://github.com/openzipkin/zipkin-api/blob/0.2.1/zipkin.proto) is considered to be more efficient than JSON, even compared to the v2's JSON (openzipkin/zipkin#2589 (comment)). This is an effort to rework envoyproxy/envoy#6798.

The approach is by serializing the v1 model to both v2 JSON and protobuf.

Risk Level: Low, since the default is still HTTP-JSON v1 based on https://github.com/openzipkin/zipkin-api/blob/0.2.2/zipkin-api.yaml.
Testing: Unit testing, manual integration test with real Zipkin collector server.
Docs Changes: Added
Release Notes: Added
Fixes: #4839

Signed-off-by: Dhi Aurrahman <dio@tetrate.io>
Signed-off-by: José Carlos Chávez <jcchavezs@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 6c6e18e5881936405cba72e936ecd6a5b3fe0852

bazel/repositories.bzl

@@ -38,6 +38,11 @@ def api_dependencies():
         locations = REPOSITORY_LOCATIONS,
         build_file_content = KAFKASOURCE_BUILD_CONTENT,
     )
+    envoy_http_archive(
+        name = "com_github_openzipkin_zipkinapi",
+        locations = REPOSITORY_LOCATIONS,
+        build_file_content = ZIPKINAPI_BUILD_CONTENT,
+    )
 
 GOGOPROTO_BUILD_CONTENT = """
 load("@com_google_protobuf//:protobuf.bzl", "cc_proto_library", "py_proto_library")
@@ -153,3 +158,23 @@ filegroup(
 )
 
 """
+
+ZIPKINAPI_BUILD_CONTENT = """
+
+load("@envoy_api//bazel:api_build_system.bzl", "api_proto_library", "api_go_proto_library")
+load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+
+api_proto_library(
+    name = "zipkin",
+    srcs = [
+        "zipkin-jsonv2.proto",
+        "zipkin.proto",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+api_go_proto_library(
+    name = "zipkin",
+    proto = ":zipkin",
+)
+"""

bazel/repository_locations.bzl

@@ -21,6 +21,9 @@ KAFKA_SOURCE_SHA = "ae7a1696c0a0302b43c5b21e515c37e6ecd365941f68a510a7e442eebddf
 UDPA_GIT_SHA = "4cbdcb9931ca743a915a7c5fda51b2ee793ed157"  # Aug 22, 2019
 UDPA_SHA256 = "6291d0c0e3a4d5f08057ea7a00ed0b0ec3dd4e5a3b1cf20f803774680b5a806f"
 
+ZIPKINAPI_RELEASE = "0.2.2"  # Aug 23, 2019
+ZIPKINAPI_SHA256 = "688c4fe170821dd589f36ec45aaadc03a618a40283bc1f97da8fa11686fc816b"
+
 REPOSITORY_LOCATIONS = dict(
     bazel_skylib = dict(
         sha256 = BAZEL_SKYLIB_SHA256,
@@ -62,4 +65,9 @@ REPOSITORY_LOCATIONS = dict(
         strip_prefix = "kafka-2.2.0-rc2/clients/src/main/resources/common/message",
         urls = ["https://github.com/apache/kafka/archive/2.2.0-rc2.zip"],
     ),
+    com_github_openzipkin_zipkinapi = dict(
+        sha256 = ZIPKINAPI_SHA256,
+        strip_prefix = "zipkin-api-" + ZIPKINAPI_RELEASE,
+        urls = ["https://github.com/openzipkin/zipkin-api/archive/" + ZIPKINAPI_RELEASE + ".tar.gz"],
+    ),
 )

envoy/config/trace/v2/trace.proto

@@ -65,6 +65,7 @@ message LightstepConfig {
   string access_token_file = 2 [(validate.rules).string.min_bytes = 1];
 }
 
+// Configuration for the Zipkin tracer.
 message ZipkinConfig {
   // The cluster manager cluster that hosts the Zipkin collectors. Note that the
   // Zipkin cluster must be defined in the :ref:`Bootstrap static cluster
@@ -80,9 +81,34 @@ message ZipkinConfig {
   // trace instance. The default value is false, which will result in a 64 bit trace id being used.
   bool trace_id_128bit = 3;
 
-  // Determines whether client and server spans will shared the same span id.
+  // Determines whether client and server spans will share the same span context.
   // The default value is true.
   google.protobuf.BoolValue shared_span_context = 4;
+
+  // Available Zipkin collector endpoint versions.
+  enum CollectorEndpointVersion {
+    // Zipkin API v1, JSON over HTTP.
+    // [#comment: The default implementation of Zipkin client before this field is added was only v1
+    // and the way user configure this was by not explicitly specifying the version. Consequently,
+    // before this is added, the corresponding Zipkin collector expected to receive v1 payload.
+    // Hence the motivation of adding HTTP_JSON_V1 as the default is to avoid a breaking change when
+    // user upgrading Envoy with this change. Furthermore, we also immediately deprecate this field,
+    // since in Zipkin realm this v1 version is considered to be not preferable anymore.]
+    HTTP_JSON_V1 = 0 [deprecated = true];
+
+    // Zipkin API v2, JSON over HTTP.
+    HTTP_JSON = 1;
+
+    // Zipkin API v2, protobuf over HTTP.
+    HTTP_PROTO = 2;
+
+    // [#not-implemented-hide:]
+    GRPC = 3;
+  }
+
+  // Determines the selected collector endpoint version. By default, the ``HTTP_JSON_V1`` will be
+  // used.
+  CollectorEndpointVersion collector_endpoint_version = 5;
 }
 
 // DynamicOtConfig is used to dynamically load a tracer from a shared library