ENH: allow arbitrary json strings to be read for event selection

To support more glob-able strings, e.g., "/home/rp.o4/catalogs/GWTC-2.1/data-release/*GW1[5,7]*_cosmo.h5", I needed to switch to a json reader rather than the bilby_pipe version. This wound up introducing an overhead because bilby_pipe aggressively strips quotes from strings which makes them no longer valid json, which is a pain.

For this specific example I can add the needed quotes back in, but it's pretty ugly.