Add service to read checkpoint folder

[kevinwallimann]

Background
The goal is to prevent Hyperdrive job instance creations when there are no messages available on a kafka topic (or only a few). To that end, the offsets from the checkpoint folder should be compared with the latest offsets from the kafka topic.

This issue is about getting the offsets from the checkpoint folder.

All configurations (including keytab location) needed to access the checkpoint folder should be available from the resolved job definition.

Task
A service method should be written, that takes a ResolvedJobDefinition and returns the latest offset from the checkpoint. The method should also return whether or not the offset has been committed.

Related
#688, #690

New application properties
kafka.consumers.cache.size Optional, default 50