[Enhancement] Add support for async fetching of metadata for a batch of shards

[amkhar]

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

Description
As part of node drop and joins, we fetch the metadata of unassigned shards on per shard basis.

OpenSearch/server/src/main/java/org/opensearch/gateway/AsyncShardFetch.java

Line 74 in c25c175

public abstract class AsyncShardFetch<T extends BaseNodeResponse> implements Releasable {

AsyncShardFetch takes care of fetching the data for a single shard. We need to add support for fetching this metadata for a batch of shards.

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.