add index label to prometheus metric #4127

Job	Run time
Coverage	6m 37s
build-and-test (ubuntu-latest, 1.17)	56s
build-and-test (ubuntu-latest, 1.18, true)	3m 39s
build-and-test (ubuntu-latest, 1.18, true)	4m 13s
performance-test-suite-detect-runners	1s
Run Gosec Security Scanner	1m 32s
build-and-test (ubuntu-latest, 1.19, true)	3m 18s
build-and-test (windows-latest, 1.18, true, true)	2m 3s
build-and-test (macos-latest, 1.18, true)	1m 31s
Coverage	1m 5s
Performance Test Suite (benchmark)	3m 35s
Performance Test Suite (jenkins)	3m 31s
	32m 1s

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