Expose configuration option to select which link type to use

[chaubold]

Problem description

Environments are constructed by linking the respective packages from the cache in the environment folder. If multiple environments use the same packages, they all link to the same package in the cache.

Rattler currently uses reflinks or hardlinks by default, and thus also Pixi.

In a Docker container, there can be an issue with hardlinks though:

If multiple environments are created with separate RUN commands in the Dockerfile, they end up in separate layers. Hardlinking between Docker image layers does not work, so Docker duplicates the files and creates full copies, blowing up the image size.

It would be great to have an option to force Pixi to use symlinks, because these do work across Docker image layers. I've created a corresponding feature request in rattler which could then be exposed by Pixi.

[chaubold]

I found a feature request that goes in a similar direction, maybe they can be addressed together: #3149