Support .node-version by default

[stevelacey]

Description:
In addition to supporting the node-version and node-version-file inputs, the workflow should check .node-version when neither input is supplied, and only fallback to latest if neither input was supplied, and that file does not exist.

Justification:
Specifying node-version/node-version-file in every setup-node usage is tedious and inconsistent with other setup-{lang} actions which usually check a version file by default in addition to supporting a {lang}-version-file input.

The setup-python and setup-ruby actions already do this, they use .python-version/.ruby-version files if they exist and no inputs are passed, and setup-php will automatically use .php-version once shivammathur/setup-php#690 is released.

Are you willing to submit a PR?
Yes, absolutely, it may be worth supporting .nvmrc too given it's popularity, but maybe that's contentious, I haven't found any other actions that support a version manager's version file, though IIRC Heroku does honor it.

[MaksimZhukov]

Hello @stevelacey ! Thank you for the suggested idea!
We will consider adding this feature and will let you know as soon as we have any decision.

[amq]

For comparison, ruby/setup-ruby supports this:
https://github.com/ruby/setup-ruby#supported-version-syntax

[taylorkline]

@MaksimZhukov I am dropping by, not to +1, but to ask if there are any updates on the follow-up:

We will consider adding this feature and will let you know as soon as we have any decision.

Thanks in advance!