Add CI for react-native-macos-init

[tom-un]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

This change adds a CI pipeline test for the react-native-macos-init command. It is based on the CI pipeline test for the react-native-windows-init command.

It starts a Verdaccio npm proxy server, published both the react-native-macos and react-native-macos-init packages to the proxy, and then tests the npx react-native init testcli and npx react-native-macos-init commands.

It does not yet test the actually building and execution of the resulting macOS test app. The CI test script will be expanded to including build and testing and the same time the local-cli is extended with a run-macos command in a future PR.

Microsoft Reviewers: Open in CodeFlow

[pull-bot]

	Messages
📖	📋 Missing Changelog - Can you add a Changelog? To do so, add a "## Changelog" section to your PR description. A changelog entry has the following format: [CATEGORY] [TYPE] - Message. CATEGORY may be: General iOS Android JavaScript Internal (for changes that do not need to be called out in the release notes) TYPE may be: Added, for new features. Changed, for changes in existing functionality. Deprecated, for soon-to-be removed features. Removed, for now removed features. Fixed, for any bug fixes. Security, in case of vulnerabilities. MESSAGE may answer "what and why" on a feature level. Use this to briefly tell React Native users about notable changes.
📖	📋 Missing Test Plan - Can you add a Test Plan? To do so, add a "## Test Plan" section to your PR description. A Test Plan lets us know how these changes were tested.
📖	📋 Missing Summary - Can you add a Summary? To do so, add a "## Summary" section to your PR description. This is a good place to explain the motivation for making this change.

Generated by 🚫 dangerJS against ba2d341

[acoates-ms]

Can be done separately, but we should look at getting this to 12