Add option to skip npm install completely

[imolorhe]

I am using this action in a step after I have already installed the node modules for my package. I don't want to install the node modules again. In my case, I'm using a mono repo where the packages are bootstrapped (lerna bootstrap) to use the versions only available locally and not yet published to npm. Running yarn within the package directory tries to download the new version from the registry and fails.

[blueedgetechno]

+1