feat: allow modifying gradlew args in hooks

[rigor789]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included. Updated the test to inject the hookService stub.

What is the current behavior?

There is no way to add additional gradlew parameters to a build.

What is the new behavior?

We can now create before-build-task-args hooks where we can modify the args array that's passed to gradlew.

For example, to use wix/Detox - we need to alter a projects app.gradle and build the app with assembleAndroidTest passed to gradlew. To do this, we have to manually run tns prepare android and then run the correct gradlew command with our additional parameters. With this change, we can do this with a hook (would need to add a condition in a real app):

module.exports = function(hookArgs, $errors, $injector) {
    hookArgs.args.unshift('assembleAndroidTest')
    hookArgs.args.push('-DtestBuildType=debug')
}

Implements #2481