kmeta package: ChildName function produces invalid resource names

[KauzClay]

Expected Behavior

When I use ChildName to create a truncated resource name, I expect the name produced to be a valid resource name in kubernetes.

Actual Behavior

The function will produce an invalid resource name ending with .

Steps to Reproduce the Problem

I've set up a go playground example with my input that cause the problem: https://go.dev/play/p/HB42UPAWp7h

Additional Info

This came up as an error in the net-contour controller that looks like this:

{"severity":"ERROR","timestamp":"2022-12-08T19:13:48.437648502Z","logger":"net-contour-controller","caller":"controller/controller.go:566","message":"Reconcile error","commit":"041f9e3","knative.dev/controller":"knative.dev.net-contour.pkg.reconciler.contour.Reconciler","knative.dev/kind":"networking.internal.knative.dev.Ingress","knative.dev/traceid":"ec12c38a-f1ac-4581-aae5-2350b60211a2","knative.dev/key":"cody/foo-java","duration":"18.23483ms","error":"HTTPProxy.projectcontour.io \"foo-java-contour-5f549ae3e6f584a5f33d069a0650c0d8foo-java.cody.\" is invalid: metadata.name: Invalid value: \"foo-java-contour-5f549ae3e6f584a5f33d069a0650c0d8foo-java.cody.\": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')","stacktrace":"knative.dev/pkg/controller.(*Impl).handleErr\n\tknative.dev/pkg@v0.0.0-20221011175852-714b7630a836/controller/controller.go:566\nknative.dev/pkg/controller.(*Impl).processNextWorkItem\n\tknative.dev/pkg@v0.0.0-20221011175852-714b7630a836/controller/controller.go:543\nknative.dev/pkg/controller.(*Impl).RunContext.func3\n\tknative.dev/pkg@v0.0.0-20221011175852-714b7630a836/controller/controller.go:491"}

net-contour uses ChildName here: https://github.com/knative-sandbox/net-contour/blob/main/pkg/reconciler/contour/resources/httpproxy.go#L275

[dprotaso]

related/dupe of #2551