feat: decouple Linux's `build` command from GitLab and introduce new features

[EricRibeiro]

Motivation

Closes #34

Changes

• Stop using GitLab's build script
• Add support for a custom build-method and custom-parameters
• Include a new test for both parameters

Notes

Down the road, we might want to move test and prepare-env away from GitLab too. Since they don't require any custom behaviour, I'll leave them for now.