Add unbound option to Adguard Home installation

[ronlut]

Pretty straightforward, like done in #2425 for Pihole.
I would happily work on it myself, if it sounds like a good idea.
I just need some structuring guidelines - I think I would extract the unbound installation and configuration to a single script, where would you place it and how to invoke it from an X-install.sh script? Does that make sense?
LMKWYT, Thanks!

[thiagohflima]

Up! 👍

[purple-emily]

This is exactly what I was looking for!

[MatKlein]

I just set that up on two nodes with Docker, combined with keepalived for high availability, but have issues with IPv6. Would also be happy about an option with a helper script.

[gigi2006]

realy good idea, plaese update this :)

[ianalexis]

UPalala