Add telemetry_span_context following conventions (#1128)

Absinthe's telemetry events includes `id` metadata, as means to
correlate start/stop/exception events. Telemetry defines a
`telemetry_span_context` for this same reasons.

This patch publishes the same `id` value  as both keys, sowe maintain
backwards compatibility as well keep adherent to conventions, for tools
that rely on that - like OpenTelemetry.

The `telemetry_span_context` is generated using `:erlang.make_ref/0`.
Given typespecs describe as `term`, should be safe to use the same value
as `id`.

lib/absinthe/middleware/batch.ex

@@ -160,7 +160,14 @@ defmodule Absinthe.Middleware.Batch do
   @batch_stop [:absinthe, :middleware, :batch, :stop]
   defp emit_start_event(system_time, batch_fun, batch_opts, batch_data) do
     id = :erlang.unique_integer()
-    metadata = %{id: id, batch_fun: batch_fun, batch_opts: batch_opts, batch_data: batch_data}
+
+    metadata = %{
+      id: id,
+      telemetry_span_context: id,
+      batch_fun: batch_fun,
+      batch_opts: batch_opts,
+      batch_data: batch_data
+    }
 
     :telemetry.execute(
       @batch_start,

lib/absinthe/middleware/telemetry.ex

@@ -16,7 +16,7 @@ defmodule Absinthe.Middleware.Telemetry do
     :telemetry.execute(
       @field_start,
       %{system_time: system_time},
-      %{id: id, resolution: resolution}
+      %{id: id, telemetry_span_context: id, resolution: resolution}
     )
 
     %{
@@ -49,6 +49,7 @@ defmodule Absinthe.Middleware.Telemetry do
       %{duration: end_time_mono - start_time_mono},
       %{
         id: id,
+        telemetry_span_context: id,
         middleware: middleware,
         resolution: resolution
       }

lib/absinthe/phase/telemetry.ex

@@ -23,7 +23,7 @@ defmodule Absinthe.Phase.Telemetry do
     :telemetry.execute(
       @operation_start,
       %{system_time: system_time},
-      %{id: id, blueprint: blueprint, options: options}
+      %{id: id, telemetry_span_context: id, blueprint: blueprint, options: options}
     )
 
     {:ok,
@@ -42,7 +42,7 @@ defmodule Absinthe.Phase.Telemetry do
     :telemetry.execute(
       @subscription_start,
       %{system_time: system_time},
-      %{id: id, blueprint: blueprint, options: options}
+      %{id: id, telemetry_span_context: id, blueprint: blueprint, options: options}
     )
 
     {:ok,
@@ -59,7 +59,7 @@ defmodule Absinthe.Phase.Telemetry do
       :telemetry.execute(
         @subscription_stop,
         %{duration: end_time_mono - start_time_mono},
-        %{id: id, blueprint: blueprint, options: options}
+        %{id: id, telemetry_span_context: id, blueprint: blueprint, options: options}
       )
     end
 
@@ -73,7 +73,7 @@ defmodule Absinthe.Phase.Telemetry do
       :telemetry.execute(
         @operation_stop,
         %{duration: end_time_mono - start_time_mono},
-        %{id: id, blueprint: blueprint, options: options}
+        %{id: id, telemetry_span_context: id, blueprint: blueprint, options: options}
       )
     end