Draft: Add email address to user state struct

The mailman integration requires an email address to be available to check if an Arch staff is a member of a mailing list.

Current plan:

Only implement the functionality for the @archlinux.org email addresses leave the other addresses alone for now, so:

• Add arch_email field to Keycloak
• Implement gluebuddy subscribing
• Write wiki instructions about how to manage your subscription (so turn off delivery of @archlinux.org email) to Staff Services
• At a later time consider adding a mailinglist field which can use a personal email address as the main keycloak email address can be changed by users themself.