Improve copying over data from idToken

Depending on the login method, the user's idToken already potentially contains some relevant information that we could use to pre-fill the registration form. We are currently just using the user's name and email from the idToken, but we could just as well use the following:

- LinkedIn profile URL (if logging in with LinkedIn)
- GitHub profile URL (if logging in with GitHub)
- Something else? (Check what kinds of fields the idToken contains / could contain)

This should be implemented by just making the correct mapping from the idToken value to the respective question in [registration-fields.js](https://github.com/hackjunction/hackplatform/blob/dev/shared/constants/registration-fields.js), see e.g. the following example with the email field for reference:

```
email: {
...FieldProps.email,
category: Categories.basicDetails,
// Here is where we map the values from the idToken
default: (userProfile, idToken) => userProfile.email || idToken.email || '',
validationSchema: required => {
const base = yup
.string()
.email()
.label(FieldProps.email.label);
return required ? base.required() : base;
}
},
```

Comienza en shared/constants/registration-fields.js, usando el mapeo predeterminado del campo de correo electrónico como referencia. Inspecciona qué campos puede contener idToken para cada método de inicio de sesión y, después, asigna las URL de perfil compatibles u otros valores útiles a las preguntas de registro correspondientes. El trabajo estará terminado cuando el formulario de registro se complete previamente con los datos disponibles de idToken sin reemplazar los valores existentes de userProfile.

Escrito por el modelo de indexación a partir del texto del issue.