feat: add X-React-Native-Project-Root header to dev server

[szymonrybczak]

Summary

To properly support @react-native-community/cli a dev server needs to return a header called X-React-Native-Project-Root with path to the project root.

Before:

❯ yarn ios
yarn run v1.22.19
$ react-native run-ios
info Another process is running on port 8081.
? Use port 8082 instead? › - Use arrow-keys. Return to submit.
❯   Yes
    No

After:

❯ yarn ios
yarn run v1.22.19
$ react-native run-ios
info A dev server is already running for this project on port 8081.

Test plan

1. Bootstrap project with npx react-native@latest init
2. Do all necessary steps to setup vxrn inside project
3. Start a dev server, and run yarn ios -> RN CLI should detect dev server on selected port.

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Name	Status	Preview	Comments	Updated (UTC)
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[szymonrybczak]

@natew wdyt about adding example to repo with bare React Native Community CLI setup?

[natew]

down for that definitely.