Add optional tag for relative bkg systematic normalisation uncertainty

Release notes

Add option to include a relative background normalisation uncertainty in gridscanner

Details

See #384 (closed)

• Small caveat is that the python script to execute the gridscanner (e.g. https://gitlab.cern.ch/atlas-phys/exot/lpx/exot-2020-06-projects/ssWWAnalysisCode/-/blob/master/tools/runGridScanner.py) will need to be modified to use this new function. But this is external to CAF

Closes #384 (closed)