Add support for build templates (and pixi)

[pditommaso]

trafficstars

This PR adds the support for build templates that allows supporting multiple container build strategies.

The first template will allow the building of container images using Conda packages using Pixi as build tool.

[robnewman]

@munishchouhan What's the status on this? What does it take to get this over the line? Thanks.

[munishchouhan]

@munishchouhan What's the status on this? What does it take to get this over the line? Thanks.

@robnewman this needs some changes and mainly testing. I will be working on this in coming weeks