Add pixi to dx for conda support

[castrojo]

First class access to the conda ecosystem has become more important for us (AI tools, etc). We ship this in lts already: https://github.com/ublue-os/bluefin-lts/blob/main/build_scripts/overrides/aarch64/05-pixi.sh

Also upstream is engaged with helping out a user on our forums and that's awesome. Docs bullet will read something like:

• Pixi for integrated conda support

Or whatever upstream feels is a more apt description.