[chore][mdatagen] Use MustNewType for metadata.Type #25876

Job	Run time
collector-build	5m 40s
docker-build	5m 57s
supervisor-test	1m 0s
kubernetes-test-matrix (v1.26.0, receiver/k8sclusterreceiver)	4m 41s
kubernetes-test-matrix (v1.26.0, processor/k8sattributesprocessor)	3m 17s
kubernetes-test-matrix (v1.26.0, receiver/kubeletstatsreceiver)	4m 14s
kubernetes-test-matrix (v1.26.0, receiver/k8sobjectsreceiver)	3m 8s
kubernetes-test-matrix (v1.25.3, receiver/k8sclusterreceiver)	4m 50s
kubernetes-test-matrix (v1.25.3, processor/k8sattributesprocessor)	3m 36s
kubernetes-test-matrix (v1.25.3, receiver/kubeletstatsreceiver)	4m 37s
kubernetes-test-matrix (v1.25.3, receiver/k8sobjectsreceiver)	3m 23s
kubernetes-test-matrix (v1.24.7, receiver/k8sclusterreceiver)	4m 49s
kubernetes-test-matrix (v1.24.7, processor/k8sattributesprocessor)	3m 41s
kubernetes-test-matrix (v1.24.7, receiver/kubeletstatsreceiver)	4m 14s
kubernetes-test-matrix (v1.24.7, receiver/k8sobjectsreceiver)	3m 12s
kubernetes-test-matrix (v1.23.13, receiver/k8sclusterreceiver)	4m 46s
kubernetes-test-matrix (v1.23.13, processor/k8sattributesprocessor)	3m 20s
kubernetes-test-matrix (v1.23.13, receiver/kubeletstatsreceiver)	4m 28s
kubernetes-test-matrix (v1.23.13, receiver/k8sobjectsreceiver)	3m 24s
kubernetes-test	1s
	1h 16m 18s

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