Remove 1.414 snr threshold

Related to #43, #53, #51

This adds a feature flag to allow non coherent triggers (i.e. whether or not to remove the 1.4 snr threshold). Wasn't sure what else to call it, but without it, we suppress triggers where only one detector had > low SNR.

Tests

With the feature flag disabled, I get the same results as an old version of O4 dev: allow_non_coh_disabled.log

With the flag enabled, I see ~ 37% more triggers (after clustering):

and ... 2276% more triggers before clustering:

The FARs were based on a background run without the flag, but that doesn't account for the huge increase in triggers. It's possible that this is expected behaviour, I'll have to check, but I expected more like a 20% increase.