component email-gateway: first draft: Initial implementation of the Email Gateway. This component uses XEP-0100 for registration. Upon registration and subsequent startups, a connection is made to registered IMAP services, and incoming emails (in `INBOX` mailboxes) are immediately forwarded as XMPP messages. In the opposite direction, an SMTP connection is established to send emails on incoming XMPP messages. rel 449

this certificates are used to enable TLS during tests. Those must be the same as in
backend_e2e (they are generated there)