docker (demo): fix starting + better UX:

- Use the new `wait_for_service` option to be sure that Prosody is launched.
- Use the new `init_script_path` option to initiate forums and bookmark a demo room.
- Activate MUC service.
- Change log formats to make them more readable.

docker/prosody-e2e/prosody.cfg.lua

@@ -109,11 +109,11 @@ VirtualHost "server2.test"
 
 VirtualHost "server3.test"
 
--- Component "muc.server1.test" "muc"
--- 	modules_enabled = {
--- 		"muc_mam";
--- 		"vcard";
--- 	}
+Component "chat.server1.test" "muc"
+ 	modules_enabled = {
+ 		"muc_mam";
+ 		"vcard";
+ 	}
 
 Component "pubsub.server1.test"
 	component_secret = "test_e2e"