[Minor] auth.signInWithOtp improvement

[vyas-meet]

This method generates a user on the fly (unless we prevent it by passing a boolean), or simply allows an existing user to sign in with a magic link.

We can also pass in metadata, but it is only relevant when a new user signs up. Otherwise, it goes into the void, not being used at all. This leads to inconsistencies and to deal with it, you need multiple DB calls like first check whether a user exists or not, and alike.

On a successful execution, it currently returns the following:

  "data": {
    "user": null,
    "session": null
  },

This is far from useful. It'd help if we at least get two parameters like:

"data": {
 userId: "uuid",
 isNewUser: true,
}

These will help us process the user further if required, again considering the fact that the metadata is not handled if it's a login and not signup.