Add samples metadata information to TH1I in output

This MR adds a TH1I called metadata to the output file with sample information (dataType, mc campaign and DSID), as the one in the picture.

This MR is related with issue #99 but does not close it completely.

We are considering a format compatible with downstream framework for ttHH. So ideally we would want the keep the order of these three bins to be maintained, but there is no problem extending the histogram with more bins with additional information.