thrift: sniffing thrift filter with request/response stats (#3622)

Glues together code from previous PRs into a ThriftFilter that counts requests (by type) and responses (by type and result), counts protocol errors for requests and responses, and records timings of request/response pairs.

Risk Level: Low
Testing: unit and manual testing
Docs Changes: trivial documentation of thrift config
Release Notes: introduced envoy.thrift filter
Relates to: #2247

Signed-off-by: Stephan Zuercher <stephan@turbinelabs.io>

Mirrored from https://github.com/envoyproxy/envoy @ 4521e89da33ce44ebdc61b2b1da07712341d743d

envoy/extensions/filters/network/thrift_proxy/v2alpha1/BUILD

@@ -0,0 +1,8 @@
+load("//bazel:api_build_system.bzl", "api_proto_library")
+
+licenses(["notice"])  # Apache 2
+
+api_proto_library(
+    name = "thrift_proxy",
+    srcs = ["thrift_proxy.proto"],
+)

envoy/extensions/filters/network/thrift_proxy/v2alpha1/README.md

@@ -0,0 +1 @@
+Protocol buffer definitions for the Thrift proxy.

envoy/extensions/filters/network/thrift_proxy/v2alpha1/thrift_proxy.proto

@@ -0,0 +1,13 @@
+syntax = "proto3";
+
+package envoy.extensions.filters.network.thrift_proxy.v2alpha1;
+option go_package = "v2";
+
+import "validate/validate.proto";
+
+// [#protodoc-title: Extensions Thrift Proxy]
+// Thrift Proxy filter configuration.
+message ThriftProxy {
+  // The human readable prefix to use when emitting statistics.
+  string stat_prefix = 1 [(validate.rules).string.min_bytes = 1];
+}