Fixed-target luminosity lines (e-p scattering)

In Run 3 a direct method will be used for the target density calibration as baseline. However, it is important to perform a cross-check with the e-p elastic scattering method as successfully used in Run 2 (see LHCb-PAPER-2018-031 and in particular section 9 of the ANA note).

Two simple lines are required for such a calibration sample:

1. A line that triggers when the number of VELO tracks is between 1 and ~10. Such a line should probably be restricted to BE crossings.
2. A NoBias line that triggers on BE crossings (to measure the trigger efficiency of the above).