containerEnv and VScode settings based on features -> options

[audacioustux]

I'm aware of this issue #164 ... but it's also necessary for me to be able to interpolate vscode settings with options value. This devcontainer-feature.json may give an insight on what i'm trying to achieve/refactor...
https://github.com/audacioustux/CompaaS/blob/b70e0b78d32c161a532411886e921e3f72731dc2/.devcontainer/local-features/graalvm/devcontainer-feature.json#L23

for now, i had to remove the configurability of the path /opt/graalvm

any other good option?