How to benchmark lumino branches/forks?

### Problem

Running benchmarks against custom branches of JupyterLab is a pleasant experience, but benchmarking against custom lumino forks seems tricky. Can we benchmark JupyterLab against a lumino fork/branch?

### Proposed Solution

We could add another parameter to the GitHub Action, which would result in using lumino from given fork/branch.

I initially thought about a local NPM registry overwriting the published lumino versions, but probably we should just make use of: https://jupyterlab.readthedocs.io/en/stable/developer/contributing.html#linking-unlinking-packages-to-jupyterlab

### Additional Context

@fcollonval I wonder what was your workflow for https://github.com/jupyterlab/lumino/pull/231- was your benchmarking automated or fully manual?