provide option to asimov whether dingo or dingo-is samples should be loaded

[jonaswildberger]

          This will only check that the importance sampling has completed. Once we add the option to *not* importance sample, this should be updated to check for the correct final file.

_Originally posted by @stephengreen in https://github.com/dingo-gw/dingo/pull/131#discussion_r1172624990_