Update versions of mariadb and redis in otobo-base.yml

[bschmalhofer]

Currently docker-compose/otobo-base.yml contains hardcoded patchlevel releases of the MariaDB and Redis images. It should be checked whether these images still receive security update.

[svenoe]

We changed this to minor upgrade level.

[bschmalhofer]

While discussing this, @svenoe and me found that allowing the users to set these versions via .env would be a good idea. Let's do this in a separate issue.