[dev-client] Allow running projects without app.json

[fson]

Why

We allow bare projects to not have an app.json / app config module, but previously trying to run a project without an app.json in dev client resulted in an error.

Please define "ios.bundleIdentifier" in app.json.

How

This PR changes this so that when app.json exists, but we can detect a bundle identifier from the Xcode project, no error is thrown and we simply use the bundle identifier from the native project.

Test Plan

Created an app using npx crna -t with-dev-client, removed app.json and verified that expod run:ios works.

[linear]

ENG-655 Create app.json if it doesn't exist when using --dev-client and launching with `i` or `a` hotkeys

In BundleIdentifier.ts We try to read the bundle identifier from the native project and app config, and if the native project config exists but app config does not then we attempt to manually update the app config. Problem: if there is no app config file, we bail out with an error rather than handling it automatically:

Please define "ios.bundleIdentifier" in app.json.

You can resolve this by creating an empty app.json, but we should just create it for the user.

I assume the same problem exists when launching the dev client for Android.