Create monitoring output dir at backup

When using monitoring services like TIGMonitoring or TPGMonitoring, the output directory is created during init withtin the '_set_dir' helper function, even if we can specify a different output dir when running the 'backup' method, ending with an empty default output dir that was created at init time.

Here the goal is to change this behavior and only create the output dir at backup time, without caring if the output dir was specified during init or during backup