L2SS-1644: Split SDP datastreams into 4 to line up with LOFAR1

Jan David Molrequested to merge
L2SS-1644-split-beamlets into main

L2SS-1644: Split SDP datastreams into 4 to line up with LOFAR1 by using 4 threads for the input of an antenna field

Closes L2SS-1644

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