feat(cli): warn underlying command when using npx react-native init (#43127)

Summary:
This adds a new warning for React Native 0.74, implementing the [RFC 0759](https://github.com/react-native-community/discussions-and-proposals/blob/nc/rnf/proposals/0759-react-native-frameworks.md#the-init-command) init command changes.

- It's added inside `react-native/cli.js` to avoid warning users when actually executing `npx react-native-community/cli` commands.
- The check is fairly simple: `process.argv[2] === 'init'`. The first two args are the Node bin and the actual script bin paths.
- The message is sent over `console.warn` to avoid potentially mixing JSON with non-JSON output.

## Changelog:

[GENERAL] [ADDED] - Warn with future command when using `npx react-native init`

Pull Request resolved: https://github.com/facebook/react-native/pull/43127

Test Plan:
Any command other than `init` must not warn.

- `$ node ./path/to/react-native/cli.js init`
- `$ node ./path/to/react-native/cli.js init --help`
  - Should warn with `Running: npx react-native-community/cli init`
    ![image](https://github.com/facebook/react-native/assets/1203991/a3f5e3d2-7b59-41fe-9a53-bc9ce5a21fd1)
- `$ node ./path/to/react-native/cli.js --help`
  - Must not warn
    ![image](https://github.com/facebook/react-native/assets/1203991/97679429-db35-47f8-bdeb-33187bb167cf)

Reviewed By: cipolleschi

Differential Revision: D54063131

Pulled By: cortinico

fbshipit-source-id: c60b8b6034087b584e98b51f5bedf68a46caf44c

packages/react-native/cli.js

@@ -39,6 +39,16 @@ async function getLatestVersion(registryHost = DEFAULT_REGISTRY_HOST) {
   });
 }
 
+/**
+ * Warn when users are using `npx react-native init`, to raise awareness of the changes from RFC 0759.
+ * @see https://github.com/react-native-community/discussions-and-proposals/tree/main/proposals/0759-react-native-frameworks.md
+ */
+function warnWhenRunningInit() {
+  if (process.argv[2] === 'init') {
+    console.warn('\nRunning: npx @react-native-community/cli init\n');
+  }
+}
+
 /**
  * npx react-native -> @react-native-community/cli
  *
@@ -66,6 +76,9 @@ async function main() {
       // Ignore errors, since it's a nice to have warning
     }
   }
+
+  warnWhenRunningInit();
+
   return cli.run(name);
 }