Split streams in decodeBS test

Fixes ATR-20798 in a similar way to how !30299 (merged) fixed another test, that is by splitting the multiple-stream ByteStream file into individual streams. The decodeBS job options are adapted to allow running on one particular type of HLT output and two such jobs are added in the tests - one for the physics_Main stream and one for the calibration_CostMonitoring stream. The same changes are applied to both the build and the grid test.

cc @tamartin