Cli: Add health check for globally installed `react-native` in `doctor`

[lucasbento]

Describe the Feature

We see a lot of issues such as #955 where problems are caused because react-native and/or react-native-cli are installed globally, would be nice to have a health check to identify and remove them.

Possible Implementations

Something like is-installed-globally but for specific packages, the implementation is pretty simple so we can work on top of that.

[thymikee]

Great, thanks!

[lucasbento]

@thymikee: I was just thinking about this, it would be nice to also identify in react-native that the CLI was in a global path if the user tried to do react-native <command>, right?

[thymikee]

Yep