Automatic merge from submit-queue (batch tested with PRs 51900, 51782, 52030)

apiservers: stratify versioned informer construction

The versioned share informer factory has been part of the GenericApiServer config,
but its construction depended on other fields of that config (e.g. the loopback
client config). Hence, the order of changes to the config mattered.

This PR stratifies this by moving the SharedInformerFactory from the generic Config
to the CompleteConfig struct. Hence, it is only filled during completion when it is
guaranteed that the loopback client config is set.

While doing this, the CompletedConfig construction is made more type-safe again,
i.e. the use of SkipCompletion() is considereably reduced. This is archieved by
splitting the derived apiserver Configs into the GenericConfig and the ExtraConfig
part. Then the completion is structural again because CompleteConfig is again
of the same structure: generic CompletedConfig and local completed ExtraConfig.

Fixes #50661.