opencensus: deprecate Zipkin configuration. (#14576)

Prefer to have operators use Envoy's native Zipkin tracer, since Zipkin
implies libcurl in opencensus. Once we complete a deprecation cycle
here, we should be able to remove this source of libcurl dependency.

Part of #11816.

Risk level: Low
Testing: bazel test //test/...

Signed-off-by: Harvey Tuch <htuch@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 877d8e1f4ddd52f7a4b7bdacd3f95529469de672

envoy/config/trace/v3/opencensus.proto

@@ -72,11 +72,14 @@ message OpenCensusConfig {
   core.v3.GrpcService stackdriver_grpc_service = 13;
 
   // Enables the Zipkin exporter if set to true. The url and service name must
-  // also be set.
-  bool zipkin_exporter_enabled = 5;
-
-  // The URL to Zipkin, e.g. "http://127.0.0.1:9411/api/v2/spans"
-  string zipkin_url = 6;
+  // also be set. This is deprecated, prefer to use Envoy's :ref:`native Zipkin
+  // tracer <envoy_v3_api_msg_config.trace.v3.ZipkinConfig>`.
+  bool zipkin_exporter_enabled = 5 [deprecated = true];
+
+  // The URL to Zipkin, e.g. "http://127.0.0.1:9411/api/v2/spans". This is
+  // deprecated, prefer to use Envoy's :ref:`native Zipkin tracer
+  // <envoy_v3_api_msg_config.trace.v3.ZipkinConfig>`.
+  string zipkin_url = 6 [deprecated = true];
 
   // Enables the OpenCensus Agent exporter if set to true. The ocagent_address or
   // ocagent_grpc_service must also be set.

envoy/extensions/tracers/opencensus/v4alpha/opencensus.proto

@@ -41,7 +41,9 @@ message OpenCensusConfig {
     B3 = 4;
   }
 
-  reserved 7;
+  reserved 7, 5, 6;
+
+  reserved "zipkin_exporter_enabled", "zipkin_url";
 
   // Configures tracing, e.g. the sampler, max number of annotations, etc.
   .opencensus.proto.trace.v1.TraceConfig trace_config = 1;
@@ -68,13 +70,6 @@ message OpenCensusConfig {
   // is not provided, the default production Stackdriver address will be used.
   config.core.v4alpha.GrpcService stackdriver_grpc_service = 13;
 
-  // Enables the Zipkin exporter if set to true. The url and service name must
-  // also be set.
-  bool zipkin_exporter_enabled = 5;
-
-  // The URL to Zipkin, e.g. "http://127.0.0.1:9411/api/v2/spans"
-  string zipkin_url = 6;
-
   // Enables the OpenCensus Agent exporter if set to true. The ocagent_address or
   // ocagent_grpc_service must also be set.
   bool ocagent_exporter_enabled = 11;