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

plugins/nginx-vhosts/functions

@@ -227,8 +227,8 @@ nginx_build_config() {
 
     # setup nginx listen ports
     plugn trigger ports-configure "$APP"
-    local PROXY_PORT=$(config_get "$APP" DOKKU_PROXY_PORT)
-    local PROXY_SSL_PORT=$(config_get "$APP" DOKKU_PROXY_SSL_PORT)
+    local PROXY_PORT=$(plugn trigger ports-get-property "$APP" "proxy-port")
+    local PROXY_SSL_PORT=$(plugn trigger ports-get-property "$APP" "proxy-ssl-port")
 
     local PORT_MAP PROXY_PORT_MAP proxy_port_map
     while read -r PORT_MAP; do