Build phoenixcmake conda package in CI

• Find/create a rattler-build docker image to use in CI
  • See rattler-build github (docker command on top)
  • to build an image: start from the pixi docker image and install rattler-build inside globally as per rattler-build install instruction (perks: can use pixi to install curl and use same image to upload to channel?)
• build package in CI using rattler-build image, upload to prefix.dev channels using phoenix@projectescape.eu API key to the phoenix-dev channel.

FYI @paubert