Add test case for OVNKubernetes alerts #519

Job	Run time
linting (lint_jsonnet)	6s
editorconfig	5s
golden (capacity-alerts)	49s
test (capacity-alerts)	47s
linting (lint_yaml)	8s
test (remote-write)	52s
golden (remote-write)	53s
linting (lint_adoc)	7s
golden (user-workload-monitoring)	55s
test (user-workload-monitoring)	49s
test (capacity-alerts-with-node-labels)	48s
golden (capacity-alerts-with-node-labels)	53s
test (vsphere)	47s
golden (vsphere)	50s
test (custom-rules)	48s
golden (custom-rules)	49s
test (release-4.13)	50s
golden (release-4.13)	2m 35s
test (team-routing)	52s
golden (team-routing)	53s
test (release-4.14)	1m 5s
golden (release-4.14)	1m 15s
test (ovn-kubernetes)	51s
golden (ovn-kubernetes)	53s
	19m 40s

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