dovecot: Add shared mailbox for the mediation team

Please see [1] and [2] for a better understanding of how this works.

[1] https://doc.dovecot.org/configuration_manual/authentication/password_databases_passdb/ [2] https://doc.dovecot.org/configuration_manual/authentication/user_databases_userdb/

Fix #464 (closed)

docs/email.md

@@ -62,8 +62,8 @@ rspamadm dkim_keygen -s dkim-rsa -b 4096 -d archlinux.org -t rsa -k archlinux.or
 the ouput gives you the DNS entries to add to the terraform files.
 The keys generated need to go to the vault:
 ```
-roles/rspamd/files/archlinux.org.dkim-rsa.key
-roles/rspamd/files/archlinux.org.dkim-ed25519.key
+roles/rspamd/files/archlinux.org.dkim-rsa.key.vault
+roles/rspamd/files/archlinux.org.dkim-ed25519.key.vault
 ```
 
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