Allow new keys in pipeline generation

[andreeaflorescu]

Summary of the PR

This PR is doing a refactoring that enables us to forward the keys that we do not recognize in the JSON test description to the auto-generated pipeline. This is needed so that we have more flexibility in using new features from Buildkite. Before this change unrecognized pipeline configurations were just dropped.

More details are available in the commit messages.

Requirements

Before submitting your PR, please make sure you addressed the following requirements:

• [x] All commits in this PR are signed (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] Any newly added unsafe code is properly documented.

[andreeaflorescu]

I will need to push another change. Converting this to draft for now.