Add separate overlap threshold parameter for initial grid and grid refinement.

There are two overlap parameters in the config file overlap-threshold and overlap-thresh. rapidpe_compute_intrinsic_grid only has overlap-threshold. I don't think overlap-thresh is being used. Seems like both the initial grid and the grid refine uses overlap-threshold. I think the original purpose of these two parameters is to use overlap-threshold for the initial grid and overlap-thresh for the grid refinement. So, we need to use overlap-thresh from the config file as --overlap-threshold in the GridRefine.sub. Here is an example of GridRefine.sub /home/vinaya.valsan/rapidPE/RapidPE_RIFT_Developments/RapidPE-RIFT_forks_sample_MDC2/test_overlpthresh/output/test_overlapthresh/S190828l_test7/20220725_gstlal_20190828_G348519/GridRefine.sub

Without these two options, if we set the initial grid with a small overlap-threshold=0.4, the refinement also uses the same overlap value. But we need an option to use a small overlap in the initial region and a large value in the refinement.