Add support for User data_source by email

[scastrianni]

Checklist

• I agree to the terms within the Auth0 Code of Conduct.

Describe the problem you'd like to have solved

One of the big reasons to use a data_source is to look up a resource by some human friendly name so that you can then access all of the other properties of that data_source throughout the TF config. If I want to add a role to a user, I must have the role_id and the user_id. I can lookup the role_id by use the role data_source and specifying the role name (a human friendly name) and get the role_id from it. However, that is not the case for a user. To lookup a user_id, I need to know the user_id to use the user data_source. If I know the user_id, then there is no point in using the user data_source. Perhaps this is because the email address of the user is NOT unique. No problem, allow the developer to specifying more than just the email address until there is enough information to get a unique user out of it.

Describe the ideal solution

See above

Alternatives and current workarounds

No response

Additional context

No response