fix: exit publish command after uploading package to appstore

[Fatme]

Currently tns publish command doesn't exit as the webpack process is started in watch mode.

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
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• Tests for the changes are included.

What is the current behavior?

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].

[rosen-vladimirov]

test cli-smoke