Evaluate support for cluster-trust-bundles

# Context
In https://github.com/knative/serving/issues/14609 we added support for configuring CA trust bundles via ConfigMaps. K8s 1.30 will start to support [cluster-trust-bundles](https://github.com/kubernetes/enhancements/tree/master/keps/sig-auth/3257-cluster-trust-bundles).

We should consider supporting them in the future. There has been a discussion on [this PR](https://github.com/knative/serving/pull/14717#discussion_r1473541048) on how this could be done (volumes vs. informers). As both approaches have pros and cons, we need to revisit this discussion.

Start by reading issue 14609, the Kubernetes cluster-trust-bundles KEP, and the discussion on PR 14717 about volumes versus informers. The issue names no files or tests; done would require revisiting those approaches and establishing a concrete support direction for cluster-trust-bundles.

Written by the indexing model from the issue text.