Gmoshkin/fix plugin rpc bug

Summary

• test: test plugin RPC after expel

• fix: report error when sending RPC to expelled replicaset

• fix: used to fail sending RPC requests if replicaset consisted of 1 instance

• fix: ignore expelled instances in plugin RPC routing

• fix: used to send RPC to Expelled instances in webui back-end

• fix: ignore garbage buckets in proc_wait_bucket_count

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• Close #1076 (closed)
• Cherry-pick to: 24.6
• Docs follow-up: not necessary
• Changelog is updated