SIB1 not handling 2 search spaces per slot for SIB1

Per standard (38.213 section 13), SIB1 may be configured with searchSpaceZero to have 2 search space sets per slot (for alternating SSBs). This feature is missing in both gNB and UE code. The search space first symbol index should be 0 for even SSB indices and num_symb_coreset for odd SSB indices while it is always 0 in our code.