Setting noise threshold use for masking from config

The adequate noise threshold used for masking depends on the length of the test the user intends to carry out.

For instance at Saclay atm due to the inefficiency of the random trigger our source scans take 30hrs, which means that at 40 kHz we need to mask pixels with noise higher than few 10^-9 at least.

Therefore I suggest we make this parameter editable from the scan config directly. At the moment it is hard-coded to 1e-6 Hits/BC here: https://gitlab.cern.ch/YARR/YARR/-/blob/devel/src/libYarr/StdAnalysis.cpp#L1358

The idea would be to instead read it from the noise scan config e.g. here: https://gitlab.cern.ch/YARR/YARR/-/blob/devel/configs/scans/rd53a/diff_noisescan.json

With the default value unchanged to 1e-6 hits/BC.