[network-controller] Integrate new RPC service

[Gudahtt]

Integrate the new RPC service (#4990) into the NetworkController.

This service would be passed into the NetworkController constructor, through to the network client constructor, then to the fetch and Infura middleware. The fetch and Infura middleware would require updates in order to support this new service. The service would replace the retry logic currently in the middleware.

With this change we may be able to easily consolidate the Infura and RPC middleware as well, closing #1279. This can be considered as a secondary priority, to be left for later if it takes more work.