Is your feature request related to a problem? Please describe:
At Shopify we heavily use https://hydrogen.new for sharing and promoting the Hydrogen Framework. We recently made changes that require Node v16.5.0 or greater. If there's no way to configure stackblitz to use Node 16, we'll probably revert those changes until this issue is resolved.

Describe the solution you'd like:
We'd like a way to configure which version of NodeJS the stackblitz container runs with.

Describe alternatives you've considered:
Our alternative is to 1) not use stackblitz or 2) revert our Node 16 specific features, though this will have to be tempoarary because the features are required for our 1.0 launch.

Additional context:
Related issue: stackblitz/core#1622