Mark `@react-native/metro-config` as optional peer to fix warning (#53314)

Summary:
The `react-native/metro-config` peer was added in https://github.com/facebook/react-native/commit/fe2bcbf4ba7ce983fac0cd09727c165517b6337f / https://github.com/facebook/react-native/issues/51836 by robhogan

Side-note: It's pulled in via `react-native/community-cli-plugin` which is a direct dependency of `react-native` for the `scripts/bundle.js` script. While, for expo, we'd love to find a way to make this an optional dependency (to avoid excessive deps that `expo` replaces otherwise), for now, it's a direct dependency.

The problem here is that this isn't optional, which means:
- with auto-installing peer dependencies it is directly fulfilled (while `react-native-community/cli` is already marked as optional and skipped)
- with legacy/non-auto peer-dependencies it is flagged as missing, but in an Expo project it wouldn't make sense to install directly

This causes a **package manager regression in the form of either a peer dependency warning**, that shouldn't be fulfilled in an Expo project, or (in the best case scenario) pulls in dependencies [that a user does not need](https://npmgraph.js.org/?q=%40react-native%2Fmetro-config#zoom=w&select=exact%3A%40react-native%2Fmetro-config%400.81.0).

An error message is already in place to inform the user of this being missing when it's not installed, so marking it as optional seems appropriate.

## Changelog:

[INTERNAL] [FIXED] Mark added `react-native/metro-config` peer dependency as optional

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Pull Request resolved: https://github.com/facebook/react-native/pull/53314

Test Plan:
Warnings like the following won't occur in fresh Expo (54/preview/`next`) projects
```
warning "workspace-aggregator-484d9ec3-587b-43cb-97de-4dcce3876578 > microfoam-mobile > react-native > react-native/community-cli-plugin@0.81.0" has unmet peer dependency "react-native/metro-config@*".
```

Reviewed By: cortinico

Differential Revision: D80450287

Pulled By: robhogan

fbshipit-source-id: c622fd4c24025676c0ec74de826f863f1e291669