SL unfiltered request for B+ -> 3mu nu analysis

Unfiltered request for B^{+} \to 3 \mu \nu analysis in SL WG, with Run2 conditions and 2M events per magnet polarity and event-type, for a total of 24M events.

Event-types: 12875071 (muon channel) and 12875070 (electron channel)

Stripping version: 28r2p1 (2016), 29r2p2 (2017), 34r0p2 (2018)

cc: @pmayenco