test(webapp): provide tests in CI

- add url and page as env variables to choice where to test and update the others
- To pass a variable to a job's service, they have to be declared in the "variables" global -> doesn't work (see: [#37])
- use of the deployed image to do E2E test instead of services of gitlab

.env.template

@@ -7,4 +7,6 @@ MQTT_URL=
 MQTT_USERNAME=
 MQTT_PASSWORD=
 REST_USERNAME=
-REST_PASSWORD=
+REST_PASSWORD=
+REST_URL=
+REST_PAGE=