Document the ports for encrypted DNS and HTTP/3

[DL6ER]

Description

Adds the ports that Pi-hole v7 needs when clients use it as an encrypted resolver - DNS-over-TLS on TCP 853 and DNS-over-QUIC on UDP 853 - and the UDP port for HTTP/3 on the web interface. DNS-over-HTTPS gets no port of its own, it is served at /dns-query on the HTTPS port, which is noted in the comments.

Also adds examples/docker-compose-encrypted-dns.yml and links the new documentation page in the README.

Motivation and Context

FTL answers DoT/DoH/DoQ itself since pi-hole/FTL#2989 and pi-hole/FTL#3000, with configurable listener ports in pi-hole/FTL#3012, so a container can offer encrypted DNS to the clients in your network without a proxy in front of it - but only if the ports are published. Documentation counterpart: pi-hole/docs#1416.

This is a draft to be merged with the release of v7.0: the README and the example describe features that have not shipped yet.

How Has This Been Tested?

Not runtime-tested - this changes comments, an example file and a documentation link only. The example was checked to be valid YAML, and the repository's editorconfig-checker and codespell both pass.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[yubiuser]

I don't think we need an example compose file for encrypted DNS - our default example in the readme covers it sufficiently. But we can review again when v7 approaches.

[rdwebdesign]

Yeah... we don't need both.

I suggest to keep just one of them: or the docker-compose-encrypted-dns.yml file, or the comments and ports on the README file.