feat: Prune unused Docker images

[hazzuk]

Prerequisites

• I have searched existing and closed feature requests

Proposal

Implement a method to easily and confidently prune truly unused Docker images.

Motivation

With each Docker image update, previous versions of Docker images will remain on the system, left unused. When they really should be removed, as eventually this will become a storage problem.

Context

This process might either be part of the karo-compose stacks update workflow or be run adhoc or both.

Alternatively, we could simply provide a guide in the karo-docs, or create a script that users can run manually. But really this should be a more controlled and automated process.

Additionally, there are probably existing solutions out there that can help with this issue.