Update logic for picking active consumer for failover subscription on non-partitioned topic. (#4604)

Instead of sorting the consumers based on priority level and consumer name then pick a active consumer, which could cause subscription getting into a flaky state, where the "active" consumer joins and leaves, no consumer is actually elected as "active" and consuming the messages.
Fix logic to always pick the first consumer in the consumer list without sorting consumers. So consumers will be picked as acive consumer based on the order of their subscription.

(cherry picked from commit 22f1d7d1)