docs: metrics docs update #6697

Job	Run time
sample_operators_tests (sample-operators/metrics-processing)	7m 58s
sample_operators_tests (sample-operators/mysql-schema)	2m 54s
sample_operators_tests (sample-operators/leader-election)	3m 29s
sample_operators_tests (sample-operators/tomcat-operator)	2m 33s
sample_operators_tests (sample-operators/webpage)	3m 6s
	20m 0s

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