feat(trace): migrate dd-trace-go v1 to v2 (#7466)

- Upgrade dd-trace-go dependency to v2.2.2
- Separate Zipkin and DataDog code paths for better maintainability
- Add proper tracer shutdown through OnShutdown()
- Replace deprecated opentracer.New() with direct tracer.Start()
- Added tests

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/trace/setup.go

@@ -25,6 +25,7 @@ func setup(c *caddy.Controller) error {
 	})
 
 	c.OnStartup(t.OnStartup)
+	c.OnShutdown(t.OnShutdown)
 
 	return nil
 }