add version support

Adds support for specifying the service version using the `version` tag,
based on a span's `service_version`.

config/test.exs

@@ -12,6 +12,7 @@ config :spandex_datadog, SpandexDatadog.Test.Support.Tracer,
   sender: SpandexDatadog.Test.Support.TestApiServer,
   env: "test",
   resource: "default",
+  service_version: "v1",
   services: [
     spandex_test: :db
   ]

lib/spandex_datadog/api_server.ex

@@ -246,7 +246,8 @@ defmodule SpandexDatadog.ApiServer do
   @spec meta(Span.t()) :: map
   defp meta(span) do
     %{}
-    |> add_datadog_meta(span)
+    |> add_env_data(span)
+    |> add_version_data(span)
     |> add_error_data(span)
     |> add_http_data(span)
     |> add_sql_data(span)
@@ -255,13 +256,20 @@ defmodule SpandexDatadog.ApiServer do
     |> Enum.into(%{})
   end
 
-  @spec add_datadog_meta(map, Span.t()) :: map
-  defp add_datadog_meta(meta, %Span{env: nil}), do: meta
+  @spec add_env_data(map, Span.t()) :: map
+  defp add_env_data(meta, %Span{env: nil}), do: meta
 
-  defp add_datadog_meta(meta, %Span{env: env}) do
+  defp add_env_data(meta, %Span{env: env}) do
     Map.put(meta, :env, env)
   end
 
+  @spec add_version_data(map, Span.t()) :: map
+  defp add_version_data(meta, %Span{service_version: nil}), do: meta
+
+  defp add_version_data(meta, %Span{service_version: version}) do
+    Map.put(meta, :version, version)
+  end
+
   @spec add_error_data(map, Span.t()) :: map
   defp add_error_data(meta, %{error: nil}), do: meta
 

test/adapter_test.exs

@@ -17,6 +17,7 @@ defmodule SpandexDatadog.Test.AdapterTest do
     Enum.each(spans, fn span ->
       assert span.service == :spandex_test
       assert span.meta.env == "test"
+      assert span.meta.version == "v1"
     end)
   end
 

test/api_server_test.exs

@@ -46,6 +46,7 @@ defmodule SpandexDatadog.ApiServerTest do
         id: 4_743_028_846_331_200_906,
         start: 1_527_752_052_216_478_000,
         service: :foo,
+        service_version: "v1",
         env: "local",
         name: "foo",
         trace_id: trace_id,
@@ -175,6 +176,7 @@ defmodule SpandexDatadog.ApiServerTest do
             "buz" => "blitz",
             "env" => "local",
             "foo" => "123",
+            "version" => "v1",
             "zyx" => "[xyz: {1, 2}]"
           },
           "metrics" => %{
@@ -265,6 +267,7 @@ defmodule SpandexDatadog.ApiServerTest do
             "buz" => "blitz",
             "env" => "local",
             "foo" => "123",
+            "version" => "v1",
             "zyx" => "[xyz: {1, 2}]"
           },
           "metrics" => %{