Mount a config directory for redmine-mysql

This mount allows to add additional configuration, such as enabling
the native password plugin for now so that we can continue using
our database.

host-pottwal.yml

@@ -454,6 +454,7 @@
           MYSQL_DATABASE: "{{ redmine_database }}"
         volumes:
           - "{{ data_dir }}/redmine/mysql:/var/lib/mysql"
+          - "{{ data_dir }}/redmine/mysql-config:/etc/mysql/conf.d"
         networks:
           - name: redminenet
       tags: