Configurable public_addr for auto-discovered apps

[nklaassen]

What would you like Teleport to do?

The app public_addr for auto-discovered apps (k8s service discovery https://goteleport.com/docs/auto-discovery/kubernetes-applications/) should be configurable.

It would also be nice if this was not only configurable per-app, but a common domain suffix could be configured for all discovered apps, this is related to #41669

What problem does this solve?

Migrating to app access from another solution like a VPN is made easier by being able to keep the same public address for apps, instead of having to switch to the proxy subdomain address everywhere.

If a workaround exists, please include it.

It's not currently possible with auto-discovery, you would have to use manually registered apps.