Handle invalid project owner error

[barthap]

ensureProjectExists crashes with cryptic HTTP 500 in the following situation:

• I am logged in to eas-cli as userABC - this name is registered in user database
• I am inside project directory where in app.json i have different username:

{
  "owner": "userXYZ""
}

• User userXYZ doesn't exists on www
• When ensureProjectExists is called, it tries to create non existing project @userXYZ/my-app and fails with HTTP 500 with no message

We should handle these cases in some way and at least show a proper error message.

[dsokal]

 dsokal@Dominiks-MacBook-Pro  ~/work/expo/example-apps/teecee   main  eas_dev build
✔ Select platform › All
    AssertionError: You must have access to the dominikdoesntexist account to run this command
    Code: ERR_ASSERTION