Add demo test variant

We're piggybacking on our existing integration test framework to record  demos that we can include in our docs

pkg/integration/clients/go_test.go

@@ -40,6 +40,12 @@ func TestIntegration(t *testing.T) {
 				return
 			}
 
+			// not running demoes right now. Arguably we should, but we'd need to
+			// strip away any artificial lag they use.
+			if test.IsDemo() {
+				return
+			}
+
 			t.Run(test.Name(), func(t *testing.T) {
 				t.Parallel()
 				err := f()