Replace custom bash templating with Confd and streamline entrypoint script

We use right now a custom bash templating and all this logic is implemented in the entry point script. Delegate the templating to confd and remove this logic from the entry point to make it easier to maintain and to enhance.

The entry point script was enhanced also to run with Cassandra and Newts and required

a) to run with a different startup command -c
b) to configure the time series and Cassandra endpoints correctly and also set the time storage strategy from "rrd" to "newts"

Refactoring the script to remove the necessity to set a different startup command and use the time storage strategy variable instead, cause this needs to be set anyways.