OSV.dev downstream users have a way to reason about records that are absent from OSV.dev because of failure to meet the minimum quality bar

# Problem statement

An OSV.dev user searching for a specific record by ID (either by using the shortcut URL OSV.dev/{identifier} or by searching for it from https://osv.dev/list cannot determine if the failure to find it is because the home database hasn't published it, or if the record has failed to meet OSV.dev's quality bar.

# Desired outcome

When a user searches for a record that is known to OSV.dev (either because it exists and has been imported, or exists and OSV.dev has declined to import it) they receive situation-appropriate feedback/behaviour from OSV.dev