feat: add version to welcome screen

[okwasniewski]

Summary:

This PR adds a version to the welcome screen when the user uses a custom one.

This is helpful when testing older versions of React Native (to make sure we are initializing the correct one). It also follows the scheme that Metro does welcoming us with the version. As an extension, we could potentially fetch the latest version from npm and display it but I didn't want to add additional API call. So we display version only if user passed a custom one.

Without explicit version (latest)

With explicit version

Test Plan:

Test out init command

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md

[szymonrybczak]

Thank you!