move prettier to peerDeps in eslint-config-react-native-community (#28637)

Summary:
In monorepo environment, prettier-plugin in some editor load from nearest `node_modules`. Older version of eslint-config-react-native-community includes prettier v1 in their dependencies. It cause conflict of code style inside the monorepo.

## Changelog

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[Internal] [Fixed] - move prettier to peerDependencies in eslint-config-react-native-community

Pull Request resolved: https://github.com/facebook/react-native/pull/28637

Test Plan: I think it would be good with no plan to test.

Reviewed By: yungsters

Differential Revision: D30648134

Pulled By: charlesbdudley

fbshipit-source-id: 6c01226d6e4cc37ddbc86be260563deb093758d0

packages/eslint-config-react-native-community/package.json

@@ -26,9 +26,11 @@
     "prettier": "^2.0.2"
   },
   "peerDependencies": {
-    "eslint": ">=7"
+    "eslint": ">=7",
+    "prettier": ">=2"
   },
   "devDependencies": {
-    "eslint": "7.12.0"
+    "eslint": "7.12.0",
+    "prettier": "^2.3.2"
   }
 }