Queued request controller to flush queue on network change for a domain

The selected network can change in other circumstances as well. For example if the user switches the network dropdown in the popup, according tot he designs it should also update the dapp-selected network (I know that's not implemented yet, but it will be soon).

So we may want to trigger this flushing somewhere else, which would capture both cases. e.g. when the state changes, or in a method responsible for making that state change

_Originally posted by @Gudahtt in https://github.com/MetaMask/core/pull/4064#discussion_r1526651126_

Start by locating the queued request controller and the state-change method that updates the selected network. Trace the existing network-change path and the popup network-dropdown path described in the issue, then identify a shared point for flushing the queue; done means both network-change cases consistently flush queued requests.

Written by the indexing model from the issue text.