Support OIDC defined scopes

**Problem**
Today I tried to setup a Firezone server login via Authgear. This was not succesful because Firezone requires `email` scope. In Firezone configuration it is possible to add additional scopes, but not remove email as it is required.
Authgear then gives the error: `specified scope is not allowed`.

Trying a few others IDP's, such as Auth0, Zitadel, I had no issues. I am no expert on OIDC, but I think `email` scope is a very commonly expected one.

As I am new to Authgear, please let me know if I missed something or can allow/enable `email` scope :)

**Solution**
Not sure what this would involve. First would be adding "email" to [AllowedScopes](). Then it might already work for my specific case, by including both `email` and `FullAccessScope`.
But for the good solution `email` scope should provide access to user email.

Start with pkg/lib/oauth/oidc/scopes.go and inspect AllowedScopes, then trace how requested OIDC scopes are handled for user data. Confirm whether adding email is sufficient for Authgear and define done as accepting the email scope while providing access to the user's email.

Written by the indexing model from the issue text.