Consider changing sharedmain behaviour about panic'ing when a config map is missing

That's fine. I'm slighly worried about "halt and catch fire" as a behavior when a configmap we ship has been removed. The idea of shipping them has mostly been about documentation, not about requiring them to have specific contents (or even be present) for things to function.

_Originally posted by @evankanderson in https://github.com/knative/pkg/pull/3190#discussion_r2169001114_

Start by locating the sharedmain behavior that panics when a shipped config map is missing, then read the surrounding config-map handling and related tests. Define the expected behavior for absent config maps and verify that shipped config maps remain documentation rather than required runtime inputs.

Written by the indexing model from the issue text.