add support for using and defaulting memory based settings to docker image

ColumnsStore now supports explicit memory settings for NumBlocksPct and TotalUmMemory however i believe there is not currently a way to force / override these in postConfigure.

The docker image should support 2 new env variables to allow overriding these and also default to some sensible small values like 1024m for NPB and 512m for TUM. Assuming my analysis is correct we'll need a mechanism to allow postCfg to take and default values for these (either as parameters or utilizing the values already in ColumnStore.xml (there is some logic for this in the upgrade path).