Fixes #388: disable systemd-resolved stub listener on Ubuntu

[lidopaglia]

Addresses the steps necessary to get Docker Pi-Hole working on a Docker host running Ubuntu 17.10 or later and closes #388.

Presumably this PR could also provide a working Docker Pi-Hole on other distros where systemd v229 or later is the init system and systemd-resolved has the DNSStubListener=yes enabled in /etc/systemd/resolved.conf. However, I have only tested this on a fresh instance of Ubuntu 20.04.4 LTS in a virtual machine and Ubuntu 22.04 LTS on a Raspberry Pi 3 Model B.

This PR introduces a new variable pihole_systemd_resolved_dns in example.config.yml that sets the upstream DNS provider in /etc/systemd/resolv.conf.

[stale[bot]]

This pull request has been marked 'stale' due to lack of recent activity. If there is no further activity, the PR will be closed in another 30 days. Thank you for your contribution!

Please read this blog post to see the reasons why I mark pull requests as stale.

[BrianHaak]

This fix worked for me on a Ubuntu 22.04 vm

[stale[bot]]

This issue is no longer marked for closure.

[geerlingguy]

This is a fairly large amount of configuration changes that would seem to support Ubuntu only... does it break Ubuntu 22.04 as well, or just 20.04 (and older?). I don't enjoy merging code that I don't personally need and would have to maintain over the long term.

[lidopaglia]

@geerlingguy broken on Ubuntu 22.04 and 20.04. Completely understood about the personal need and maintenance burden. Feel free to close.

[stale[bot]]

This pull request has been marked 'stale' due to lack of recent activity. If there is no further activity, the PR will be closed in another 30 days. Thank you for your contribution!

Please read this blog post to see the reasons why I mark pull requests as stale.

[stale[bot]]

This pull request has been closed due to inactivity. If you feel this is in error, please reopen the pull request or file a new PR with the relevant details.