Automatic merge from submit-queue (batch tested with PRs 47204, 46808, 47432, 47400, 47099)

Make the generic webhook admission controller use the dynamic webhook config manager

Based on #46672 and #46388.

Only the last commit is unique.

* removed `SetWebhookSource` from the PluginInitializer
* implemented `SetExternalClientset` for the generic webhook admisson controller, initializing an ExternalWebhookConfigurationManager in the method.