Mark redirect_uri optional on RedirectLoginOptions

[frederikprijck]

Description

When configuring a global redirect_uri (by passing it as a property on Auth0ClientOptions to the Auth0Client constructor), passing a redirect uri is not required when calling loginWithRedirect (I think it will even be ignored if you do so: https://github.com/auth0/auth0-spa-js/blob/master/src/Auth0Client.ts#L67).

However, the typings have marked redirect_uri as required for RedirectLoginOptions.

This PR ensures the property is marked optional.

Testing

The samples from the Angular quickstart guide don't compile for me, for example the AuthGuard has this code:

client.loginWithRedirect({
  appState: { target: state.url }
});

Which gives me the following TSC error:

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master