RealtimeProvisioningHelper does not account for deepStore

The RealtimeProvisioningHelper assumes that you need all the segments in memory in the realtime host, this isn't the case if you are pushing completed segments to deepStore. It would be nice if we could tell the realtime provisioning helper that deep store is enabled so that it can account for this.

Start by locating RealtimeProvisioningHelper and tracing how it calculates realtime-host memory for segments. Identify how deepStore is configured and where completed segments leave memory; done means the helper can be told that deepStore is enabled and adjusts its accounting accordingly, with relevant tests covering both modes.

Written by the indexing model from the issue text.