Update Pi-hole configuration to v6 (and provide notes for those upgrading)

[geerlingguy]

Pi-hole v6 is here: https://pi-hole.net/blog/2025/02/18/introducing-pi-hole-v6/

The environment variables for Docker are a bit different than previous versions—see https://docs.pi-hole.net/docker/

Hopefully it's a quick and easy shift to the new setup!

[bluttmer]

HI Jeff,

Will you need people to help test? I have a rpi 4b 8gig running ubuntu 24.04.

Ive had some issues getting to to work so not sure if that would be an issue.

Thank you again for all your great ideas and videos.

Bill

[ian-rose]

A first pass of updating the WEBPASSWORD to FTLCONF_webserver_api_password and removing ServerIP appears to be working, at least in the sense of being able to log in to the web UI. Additionally Pi-hole exporter still returns metrics. #634

[geerlingguy]

#634 seems like it should at least get initial configs working for new installs.

For existing users, it might be good to document how to upgrade cleanly.