fix: address CI failures from env var migration

- Add apps:set subcommand for managing apps properties (mirrors
  ps:set, scheduler:set, builder:set pattern)
- Update nginx-vhosts functions/pre-disable-vhost/pre-enable-vhost
  to read proxy port from properties instead of config vars
- Fix test commands to use correct property-setting approaches:
  prop binary for ports properties, apps:set for apps properties

tests/unit/apps_2.bats

@@ -116,7 +116,7 @@ teardown() {
   echo "output: $output"
   echo "status: $status"
   assert_success
-  run /bin/bash -c "dokku ports:set $TEST_APP proxy-ssl-port 443"
+  run /bin/bash -c "$PLUGIN_CORE_AVAILABLE_PATH/common/prop set ports $TEST_APP proxy-ssl-port 443"
   echo "output: $output"
   echo "status: $status"
   assert_success