Add spec for cluster stats metric and index_metric filter paths. #1543

Job	Run time
test-opensearch-spec (version=1.3.17, hub=opensearchproject, tests=default)	1m 39s
test-opensearch-spec (version=2.0.0, hub=opensearchproject, tests=default)	1m 13s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=default)	1m 33s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/index_state_management)	1m 7s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/ml)	2m 1s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=routing)	1m 20s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=snapshot)	1m 0s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/streaming)	1m 2s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/notifications)	1m 0s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/query_insights)	52s
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 29s
test-opensearch-spec (version=3.0.0, hub=opensearchstaging, tests=default)	2m 4s
merge-coverage	5s
	17m 27s

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