Enable BuildKit by setting DOCKER_BUILDKIT in the env files

[ezio-melotti]

This should fix the warning reported in:

• Fix Docker build deprecation warning #572

[Copilot]

Pull request overview

This PR enables Docker BuildKit by adding the DOCKER_BUILDKIT=1 environment variable to all environment configuration files, addressing issue #572 which likely reported a warning about BuildKit not being enabled. BuildKit is Docker's improved build system that provides better performance, caching, and build output.

• Adds DOCKER_BUILDKIT=1 to all three environment configuration files
• Refactors package installation code in simoc.py for better maintainability

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
simoc_docker_ngs.env	Adds export DOCKER_BUILDKIT=1 to enable BuildKit for the ngs.simoc.space environment
simoc_docker_beta.env	Adds export DOCKER_BUILDKIT=1 to enable BuildKit for the beta.simoc.space environment
simoc_docker.env	Adds export DOCKER_BUILDKIT=1 to enable BuildKit for the localhost environment
simoc.py	Refactors package installation by extracting package list into a variable for cleaner code

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[ezio-melotti]

This didn't work:

ERROR: BuildKit is enabled but the buildx component is missing or broken.
       Install the buildx component to build images with BuildKit:
       https://docs.docker.com/go/buildx/

Apparently BuildKit is not installed on Ubuntu 24.04 and can either be installed manually, the docker apt repo can be added and BuildKit/buildx installed from there, or we can just keep using the regular build and wait for the next version of Ubuntu to update the Docker packages.