Automated dataset qc improvements

[anngvu]

• Better summarized warning/error messages, e.g. for
  • https://github.com/nf-osi/dcc-site/issues/99#issuecomment-2469442863, should say that no dataset folders are found but there are data files
  • https://github.com/nf-osi/dcc-site/issues/1014#issuecomment-2451043379, don't show unnecessary warning
• Try harder at detecting nested datasets, going to one deeper level. This would be more consistent with our current docs, where we acknowledge that one additional level of nesting is reasonable (to organize by milestone/cohort/other types of batches within the same data type). This will help avoid false negative results for datasets with one more level of organization such as in
  • https://github.com/nf-osi/dcc-site/issues/139
  • https://github.com/nf-osi/dcc-site/issues/111