Move the command to a different package in packages/cli-hermes

[jessieAnhNguyen]

Summary:

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• Solves Move the command to its own package #8
• Move the command to a new package, but still add it as one of the projectCommands

Test Plan:

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• Test it by linking the packages as guided on Testing guide
• As we add a new package, add this into the list of linked packages "@react-native-community/cli-hermes"
• The result still looked like before
  

[jevakallio]

LGTM!

One small add, can you also add the new cli-hermes package to the yarn link list of packages in the Contributing documentation here:
https://github.com/MLH-Fellowship/cli/blob/master/CONTRIBUTING.md#yarn-v1