chore: add managed by label to namespace #2147

Job	Run time
build-api	1m 53s
build-router	1m 4s
build-test-experiment-engine-plugin	32s
build-cluster-init	16s
release-rules	3s
build-ui	1m 54s
test-engines-experiment	25s
test-engines-router	1m 13s
test-api	7m 42s
test-e2e (In-cluster credentials; API e2e)	11m 58s
test-e2e (Remote cluster credentials; SDK e2e)	13m 21s
publish / publish-router	1s
publish / publish-app	1s
	40m 23s

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