[Integ] Add integration test for Async Shard Fetch revamp

[amkhar]

Describe the bug
Original Issue opened : #5098 . This issue is a sub task for the overall project defined #8098.

Description
Today, during node drop and joins, we fetch the metadata of unassigned shards on per shard basis. As part of #8098 revamp project, we are changing the fetch from per shard to a batch of shards. Add integration tests which covers new scenarios.

Additional context
Please go through the discussion #5098 to understand the overall enhancement approach and check #8098 to see the sub tasks of overall project.