This commit introduces a new `InputLoader` policy by which, if no input is provided, we use a static default input list. We also modify the code to use this policy for dnscheck and stunreachability, with proper input. We also modify `miniooni` to pass the new `ExperimentName` field to the `InputLoader` to indicate which default input list to use. This diff is part of a set of diffs aiming at fixing https://github.com/ooni/probe/issues/1814 and has been extracted from https://github.com/ooni/probe-cli/pull/539. What remains to be done, after this diff has landed is to ensure things also work for ooniprobe and oonimkall.