Add compactor start duration in seconds metric #8116

Job	Run time
test	17m 42s
build	3m 45s
lint	19m 3s
integration-configs-db	1m 50s
integration (requires_docker)	4m 58s
integration (integration_alertmanager)	3m 49s
integration (integration_backward_compatibility)	11m 35s
integration (integration_memberlist)	7m 9s
integration (integration_querier)	12m 41s
integration (integration_ruler)	3m 36s
integration (integration_query_fuzz)	1m 53s
deploy_website	0s
deploy	0s
	1h 28m 1s

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