Make install_node optional 

Installing node/ nvm can lead to a lot of wasted ressources. We should make it optional - in particular if the project only use foundry

https://github.com/crytic/slither-action/blob/5c7580c54648c48c709498dc7acb7133a89db179/entrypoint.sh#L129C1-L149

See an example where nvm install takes forever: https://github.com/pcaversaccio/createx/actions/runs/6716947847/job/18291251493?pr=23#step:18:184