Add support for NVM_SILENT environment variable

[regulskimichal]

I'd like to add a feature that disables some messages while switching between multiple versions of node. I use powerlevel10k theme that already prints versions of node so I find it useful to make it possible to disable some verbose messages.

[raisedadead]

@lukechilds please consider merging this.

[nottmey]

@regulskimichal would be great to have this, if you can spare the time fixing the remarks