[chore][receiver/kafkametrics] Share a single franz-go admin client across all scrapers #93918

Job	Run time
docker-build	9m 52s
datadog-examples-test	6m 0s
collector-build	10m 11s
kubernetes-test-matrix (v1.34.0, processor/resourcedetectionprocessor)	10m 47s
kubernetes-test-matrix (v1.34.0, receiver/k8sclusterreceiver)	13m 12s
kubernetes-test-matrix (v1.34.0, receiver/kubeletstatsreceiver)	5m 22s
kubernetes-test-matrix (v1.34.0, receiver/k8seventsreceiver)	4m 10s
kubernetes-test-matrix (v1.34.0, receiver/k8sobjectsreceiver)	4m 41s
kubernetes-test-matrix (v1.35.0, receiver/k8seventsreceiver)	4m 14s
kubernetes-test-matrix (v1.35.0, processor/k8sattributesprocessor)	12m 37s
kubernetes-test-matrix (v1.35.0, extension/observer/k8sobserver)	3m 19s
kubernetes-test-matrix (v1.35.0, receiver/kubeletstatsreceiver)	4m 54s
kubernetes-test-matrix (v1.34.0, extension/observer/k8sobserver)	3m 23s
kubernetes-test-matrix (v1.34.0, processor/k8sattributesprocessor)	13m 41s
kubernetes-test-matrix (v1.35.0, processor/resourcedetectionprocessor)	10m 58s
kubernetes-test-matrix (v1.35.0, receiver/k8sclusterreceiver)	12m 58s
kubernetes-test-matrix (v1.35.0, receiver/k8sobjectsreceiver)	5m 32s
supervisor-test	12m 14s
kubernetes-test	2s
	2h 28m 7s

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