[FEAT]: Trillium vs Trillium-gpu: add a `same_filesystem_as` config entry

[lebrice]

Context

Trillium and trillium-gpu are actually the same physical cluster, with a shared filesystem.

In the context where we want to start to think about how to manage datasets and such, we should avoid considering them as separate.

Proposed solution

[tool.cluv.clusters.trillium]
env = { ... }

[tool.cluv.clusters.trillium-gpu]
env = { ... }
same_filesystem_as = "trillium"