Created new executable to subtract dist stats. Added the new executable to the...

This feature adds capabilities to subtract dist stats

Changes made: -

• A new folder called start_dist_stats is made which holds all dist stats before the start time provided (if any). These dist stats are subtracted from the marg_dist_stats . The DAG depends on existence of this dir
• Data discovery was made faster
• New executable called gstlal_inspiral_diststat_subtract was added which does the dist stats subtraction
• The prior_dist_stats is also passed to the executable to add it back in
• isub of HorizonHistory was changed to remove all info before specified time and not follow a key system (Might result in problems if 1 key needs to be removed)

Testing Done: -

• All of O4a Edward was reranked using the dist stats subtraction workflow. It ran without any errors, although the config looks ugly and has redundancy. This should be fixed in a later commit after consultation of motivation from previous commit. The results of the subtracted run are here. These look very similar to the non-subtracted run results here.
• The effect of subtraction was compared with some test runs using O4b data to show more pronounced effect. The non-subtracted plots for a single bin for the above test are shown here. While the subtracted plots for the same bin are shown here. The effect is more pronounced when using O4b data since a smaller time frame was chosen. Those plots can be seen here - non-subtracted plots and subtracted plots.