Add spec for cluster stats metric and index_metric filter paths. #1542

Job	Run time
test-opensearch-spec (version=1.3.17, hub=opensearchproject, tests=default)	1m 32s
test-opensearch-spec (version=2.0.0, hub=opensearchproject, tests=default)	1m 20s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=default)	1m 42s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/index_state_management)	2m 17s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/ml)	1m 49s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=routing)	1m 27s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=snapshot)	1m 10s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/streaming)	1m 6s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/notifications)	1m 15s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/query_insights)	1m 9s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/workload-management)	1m 2s
test-opensearch-spec (version=2.19.0, hub=opensearchstaging, tests=default)	1m 36s
test-opensearch-spec (version=3.0.0, hub=opensearchstaging, tests=default)	1m 36s
merge-coverage	0s
	19m 1s

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