dovecot: add custom mail namespaces for shared folders

dovecot/defaults/main.yml

@@ -40,4 +40,5 @@ dovecot_auth_default_realm: ''
 dovecot_auth_krb5_keytab: ''
 dovecot_auth_mechanisms:
   - plain
+dovecot_mail_namespaces: []
 dovecot_special_mailbox_auto_subscribe: false

dovecot/templates/conf.d/10-mail.conf.j2

@@ -79,6 +79,14 @@ namespace inbox {
   # See 15-mailboxes.conf for definitions of special mailboxes.
 }
 
+{% for namespace in dovecot_mail_namespaces %}
+namespace {
+  {% for key, value in namespace.items() %}
+  {{ key }} = {{ value }}
+  {% endfor %}
+}
+{% endfor %}
+
 # Example shared namespace configuration
 #namespace {
   #type = shared