feat: implement first-pass at networking plugin

Implements help, `rebuild`, and `rebuildall` command.

Refs #2403

plugins/network/commands

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+[[ " help network:help " == *" $1 "* ]] || exit "$DOKKU_NOT_IMPLEMENTED_EXIT"
+source "$PLUGIN_AVAILABLE_PATH/network/internal-functions"
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+
+case "$1" in
+  help | network:help)
+    network_help_cmd "$@"
+    ;;
+
+  *)
+    exit "$DOKKU_NOT_IMPLEMENTED_EXIT"
+    ;;
+
+esac