feat: add support for cloning/syncing from a remote repository

This makes it a bit easier for external projects to implement deploy webhooks by exposing the ability to sync from a git repository/sha.

plugins/git/subcommands/fetch

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+source "$PLUGIN_AVAILABLE_PATH/git/internal-functions"
+set -eo pipefail
+[[ $DOKKU_TRACE ]] && set -x
+
+cmd-git-fetch "$@"