fix(cli): simplify Metro watch mode and communicate when disabled (#20939)

# Why

Fixes ENG-7089

# How

Because this option is only exposed through `Metro.runServer`, I added
the override in

fix(cli): simplify Metro watch mode and communicate when disabled (#20939)

# Why

Fixes ENG-7089

# How

Because this option is only exposed through `Metro.runServer`, I added
the override in `@expo/cli`. Alternative, we could add a custom Metro
config option to move this to the config itself, however, that would
create a significant diversion of the normal Metro config.

> **Note**
> We could add a Metro version check and disable the warning, but I
think it's safe to skip that and leave it in for older Metro versions.
It's not really synced, but if the message pops up, it's very very
likely Metro actually is running without watch.

# Test Plan

See added tests.

# Checklist

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- [ ] Documentation is up to date to reflect these changes (eg:
https://docs.expo.dev and README.md).
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Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)
- [ ] This diff will work correctly for `expo prebuild` & EAS Build (eg:
updated a module plugin).

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