Add spec for cluster stats metric and index_metric filter path. (#639) #1545

Job	Run time
test-opensearch-spec (version=1.3.17, hub=opensearchproject, tests=default)	1m 18s
test-opensearch-spec (version=2.0.0, hub=opensearchproject, tests=default)	1m 26s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=default)	1m 39s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/index_state_management)	1m 1s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/ml)	1m 54s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=routing)	1m 15s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=snapshot)	57s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/streaming)	1m 12s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/notifications)	1m 9s
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)	51s
test-opensearch-spec (version=2.18.0, hub=opensearchproject, tests=plugins/analysis)	1m 23s
test-opensearch-spec (version=2.19.0, hub=opensearchstaging, tests=default)	1m 41s
test-opensearch-spec (version=3.0.0, hub=opensearchstaging, tests=default)	1m 45s
merge-coverage	5s
	18m 28s

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