Make perform scenario a telemetry span

Author: NelsonVides

doc/telemetry.md

@@ -2,6 +2,15 @@
 
 Amoc also exposes the following telemetry events:
 
+### Scenario
+
+A telemetry span of a full scenario execution
+```erlang
+event_name: [amoc, scenario, user]
+measurements: #{}
+metadata: #{}
+```
+
 ### Controller
 
 Indicates the number of users added or removed

src/amoc_user.erl

@@ -29,13 +29,15 @@ stop(Pid, Force) when is_pid(Pid) ->
 init(Parent, Scenario, Id, State) ->
     proc_lib:init_ack(Parent, {ok, self()}),
     process_flag(trap_exit, true),
-    perform_scenario(Scenario, Id, State).
+    ScenarioFun = fun() -> perform_scenario(Scenario, Id, State) end,
+    telemetry:span([amoc, scenario, user], #{}, ScenarioFun).
 
--spec perform_scenario(amoc:scenario(), amoc_scenario:user_id(), state()) -> ok.
+-spec perform_scenario(amoc:scenario(), amoc_scenario:user_id(), state()) -> {term(), map()}.
 perform_scenario(Scenario, Id, State) ->
-    case erlang:function_exported(Scenario, start, 2) of
-        true ->
-            Scenario:start(Id, State);
-        false ->
-            Scenario:start(Id)
-    end.
+    Ret = case erlang:function_exported(Scenario, start, 2) of
+              true ->
+                  Scenario:start(Id, State);
+              false ->
+                  Scenario:start(Id)
+          end,
+    {Ret, #{}}.