Evaluate and create plan for future of runner sandbox

Problem

Our current runner sandbox has multiple problems that can't be easily solved with iteratively evolving the current setup as outlined in gitlab-org#22766.

Desired Outcome

Create a plan for the next steps on evolving/changing our sandboxing setup. Part of this should be evaluating and grading different options.

None exhaustive list of directions worth evaluating:

1. Using Language Server based sandboxing: https://gitlab.com/groups/gitlab-org/editor-extensions/-/work_items/206
2. Nono