feat: refactor to use network plugin

- Add proxy-build-config hook to rebuild network and proxy settings for an application
- Scope nginx:build-config to work only when it is the configured proxy for an application
- Refactor deploy code to interact with network plugin for computed and actual ipaddr/port settings
- Ensure the proxy-build-config plugin trigger is called on ps:restore
- Expose a few plugin triggers for retrieving networking information for a given APP/PROC_TYPE/CONTAINER_ID combination

plugins/network/network-get-ipaddr

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+source "$PLUGIN_AVAILABLE_PATH/network/functions"
+
+network-get-container-ipaddr "$@"