chore: add managed by label to namespace #2148

Job	Run time
build-api	1m 56s
build-cluster-init	15s
build-router	59s
build-test-experiment-engine-plugin	30s
build-ui	1m 46s
release-rules	7s
test-engines-experiment	18s
test-engines-router	1m 4s
test-api	1m 37s
test-e2e (In-cluster credentials; API e2e)	11m 16s
test-e2e (Remote cluster credentials; SDK e2e)	10m 33s
publish / publish-router	1s
publish / publish-app	1s
	30m 23s

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