Support for internal-databases/redis custom configuration

[ficloc]

(Sorry i already added an issue for that (#81) but i just realise that a simple discussion may be sufficient at first)

Hi,
I'am testing icinga-stack deployment to CERN kubernetes cluster air-gapped from the internet resources.
I wonder to what extent it is possible to adapt the Helm chart to allow configuration of the image source, particularly with regard to the resources of the internal-databases (mariadb) and redis templates. Alternatively, is there already a solution that allows me to specify my own paths?