Add peak finding strategy to FindSXPeaks

[RichardWaiteSTFC]

Describe the solution you'd like Add peak finding strategy to FindSXPeaks as per SXD2001 - instead of using a threshold, look for peaks by bins that are more than n-sigma different in intensity

Also might be good to add e.g. min/max peak size (number detectors and tof bins)

Additional context