improve: add sharding sample as integration test (#3460) #7387

Job	Run time
sample_operators_tests (sample-operators/mysql-schema)	3m 43s
sample_operators_tests (sample-operators/operations)	9m 34s
sample_operators_tests (sample-operators/webpage)	4m 14s
sample_operators_tests (sample-operators/leader-election)	4m 8s
sample_operators_tests (sample-operators/tomcat-operator)	4m 9s
	25m 48s

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