Update Quad9 logging information and DNS server footnotes

[ghost]

Bigger changes

• Update Quad9 logging status from "No" to "Some"
  • Their business model is literally dependent on logging to some degree. They use data from their DNS service for threat monitoring and response analysis, which their sponsors pay for (IBM is one of those sponsors, for example). While what's logged isn't personally identifiable, I don't think it's fair to label their service as no logging. Some doesn't mean bad, as demonstrated with the same logging status applied to AdGuard and Cloudflare.
• Subsequently, add a Quad9 footnote.

Minor changes

• Update Cloudflare privacy policy link to their more relevant Public DNS Resolver Privacy page, which is an extension of their overarching privacy policy.
• Update Mullvad privacy policy link to their more relevant No Logging Data Policy page. Their main privacy policy page has no relevant information to their DNS service, nor does their other privacy pages besides the no logging one.
• Update the Mullvad footnote with more relevant information and move the footnote link to the logging column.
• Update AdGuard footnote to primarily use AdGuard as the subject instead of "we" and use quotes when necessary.
• Include privacy policy links in footnote since they're relevant and serve as a citation.
• Add "If not specifically requested by the user, no data is logged" to NextDNS footnote.
• Rephrase criteria introduction sentence

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