rtx verion file support

[pvinis]

Description: node-version-file should support rtx too. heres what .rtx.toml looks like

[tools]
yarn = "1.22.19"
nodejs = "18.16.0"

I saw the regex here doesn't work for this file.

Justification: We support a few files, let's support one more popular one.

Are you willing to submit a PR? Yes.