Add an explicit flag to skip Node.js installation

[sestrella]

Description:
After reviewing the source code, it appears that providing an empty string to the node-version input is the simplest approach to bypassing Node.js installation, which may require greater explanation in the README file. On the other hand, using an empty string to control this behaviour may be less intuitive than using a self-explanatory flag such as skip_install.

Justification:
In some cases, users may prefer to use an alternative Node.js installation method, such as Nix, while still benefiting from the caching capabilities provided by this action.

Are you willing to submit a PR?
Yes, if this proposal gets accepted.

[HarithaVattikuti]

Hello @sestrella
Thank you for creating this feature request. We will investigate it and get back to you as soon as we have some feedback.