[hotfix] add logging to capture new fingerprints

• context:

  • when we re-register channels, their fingerprints may change in ways that go undetected/updated by the DIAGNOSTICS channel
  • we would like to be able to recover from this by manually trusting the new fingerprint, but we can't b/c we can't recover the new fingerprint anywhere (it is not in any keystores that we control)

• changes:

  • whenever we detect a new fingerprint in dispatcher, log it!

• side-effects:

  • provide more granular logging of healtcheck failures in diagnostics module