refactor: ditch consumer groups for direct consumers

[kalbhor]

Apart from replacing cgs with direct consumer, this MR fixes the stop-at-end flag which wasn't functioning before

[kalbhor]

Why replace consumer-groups:

• We're not using the commit offset feature at all since all offsets are tracked in memory with initial value from the target topic
• leaveAndResetOffsets seems to fail with UNKNOWN_TOPIC sometimes when a topic is reset causing the offsets to get out of sync
• Direct consumers are easier to reason about and we do not have to care about rebalance scenarios