add node role to metrics metadata

[rishabh6788]

Description

add node role to metrics metadata to easily analyze metrics for clusters with multiple node roles.

Issues Resolved

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Testing

• New functionality includes testing

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🧪 PR contains tests

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⚡ Recommended focus areas for review Possible KeyError node_stats["roles"] is accessed unconditionally. If the node stats sample does not include a roles field (e.g., in older cluster versions or unexpected API responses), this will raise a KeyError and break metrics recording. Consider using node_stats.get("roles") with a sensible default to make this more defensive. roles = node_stats["roles"]

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Category	Suggestion	Impact
Possible issue	Safely access roles field to prevent KeyError Directly indexing node_stats["roles"] will raise a KeyError for nodes/clusters that do not return the roles field (e.g., older OpenSearch versions or restricted permissions). Use .get("roles", []) to safely handle missing keys and avoid breaking metrics collection. osbenchmark/telemetry.py [967] node_name = node_stats["name"] -roles = node_stats["roles"] +roles = node_stats.get("roles", []) metrics_store_meta_data = { "cluster": self.cluster_name, "node_name": node_name, "roles": roles } Suggestion importance[1-10]: 6 __ Why: Using .get("roles", []) is a reasonable defensive measure against missing roles keys in node stats responses, though the roles field is typically present in OpenSearch node stats responses.	Low