[Discover] Add internal state container

[kertal]

Part of #140765

Summary

We need to introduce a new state container for the internal state, that's the state used in several components but not synced with the URL (While appState and globalState are synced with the URL). This new container would contain 2 values: dataView & dataViewAdHocList, which are used in several parts of Discover

export interface InternalState {
   dataView: DataView | undefined;
   dataViewAdHocList: DataView[];
 }

This new state container would be part of DiscoverStateContainer (formerly known as GetStateReturn), preparing for the consolidation of various state-related code in a central container drafted in #140765.

This PR allows us to move forward to enable editing of data views directly in Discover like Lens #142723

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kertal]

closing in favor of #145074