Use marginalized_parameters attribute for reconstruction

I'm looking at implementing marginalization over a new parameter and found that there was a bunch of hard-coded stuff I needed to work around.

This MR should make the whole process of the reconstruction more flexible using the _marginalized_parameters attribute.

bilby/gw/conversion.py

@@ -1410,8 +1410,8 @@ def generate_sky_frame_parameters(samples, likelihood):
 
 
 def fill_sample(args):
-    marginalized_parameters = getattr(likelihood, "_marginalized_parameters", list())
     ii, sample, likelihood = args
+    marginalized_parameters = getattr(likelihood, "_marginalized_parameters", list())
     sample = dict(sample).copy()
     likelihood.parameters.update(dict(sample).copy())
     new_sample = likelihood.generate_posterior_sample_from_marginalized_likelihood()