fix: improve app check

See coop-cloud/organising#446

cli/app/upgrade.go

@@ -254,6 +254,17 @@ recipes.
 		config.SetChaosVersionLabel(compose, stackName, chosenUpgrade)
 		config.SetUpdateLabel(compose, stackName, app.Env)
 
+		envVars, err := config.CheckEnv(app)
+		if err != nil {
+			logrus.Fatal(err)
+		}
+
+		for _, envVar := range envVars {
+			if !envVar.Present {
+				logrus.Warnf("env var %s missing from %s.env, present in recipe .env.sample", envVar.Name, app.Domain)
+			}
+		}
+
 		if err := internal.NewVersionOverview(app, deployedVersion, chosenUpgrade, releaseNotes); err != nil {
 			logrus.Fatal(err)
 		}