Ability to change the Druid configuration

[spaghettifunk]

Is your feature request related to a problem? Please describe.
All the configuration files are backed into the Docker image. This is necessary for Druid to start the services. However, we want to have the possibility to change certain values depending on the case.

Describe the solution you'd like
Being able to inject the whole file as configmap with the appropriate values for each service.

Describe alternatives you've considered
An alternative would be to abstract certain parameters and pass them as ENV variable to the Service deployment so that it can be substituted by the OS.