AdGuard DNS in example config is outdated

[Russell Phillips]

Official announcement:
https://adguard.com/en/blog/adguard-dns-new-addresses.html

The stubby.yml.example file contains references to AdGuard servers that have been replaced, and will be shut down in the near future.

Another thing to note is that the official docs now reference "dns.adguard-dns.com". The existing "dns.adguard.com" still resolves to the same address, but has possibly been deprecated.
https://adguard-dns.io/en/public-dns.html

I found this issue in 22.04 Jammy, but I also checked the ubuntu/devel git branch and it has not been updated there either.

[Russell Phillips (ignissport)]

The September 2020 announcement stated plans to deactivate the old servers in the next 2 years. It's now September 2022. It hasn't happened yet, but it may be imminent.