Add compactor start duration in seconds metric #8126

Job	Run time
build	3m 46s
lint	16m 20s
test	17m 45s
integration-configs-db	1m 49s
integration (requires_docker)	5m 10s
integration (integration_alertmanager)	3m 56s
integration (integration_backward_compatibility)	11m 38s
integration (integration_memberlist)	7m 40s
integration (integration_querier)	12m 37s
integration (integration_ruler)	3m 49s
integration (integration_query_fuzz)	1m 58s
deploy	0s
deploy_website	0s
	1h 26m 28s

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