[network-controller] Validate that selected network state is recognized

[Gudahtt]

Add validation to ensure that the selected network state (providerConfig) is either a built-in network or matching a custom network configuration.

This would allow us to simplify the controller by removing all logic related to handling unrecognized provider configuration state.

[Gudahtt]

It would probably be easier to do #1462 before this

[mcmire]

Is this relevant anymore now that providerConfig has been removed?