More CustomRPC options in network dropdown list

[p-s-dev]

The network dropdown list contains Mainnet, testnets, localhost, and the last two custom RPC that were used.

If you use more than two custom RPC urls, you need to constantly go in to the Settings window and copy-paste the "New RPC URL".

It would be really nice if the Settings UI allowed for a user-defined list of RPC urls to show in the network dropdown list with "add new" and "remove from list" functions. Maybe the list of RPC Urls could contain a "visible" toggle boolean for each, which would allow the urls to be saved but not shown in the "select network" dropdown by default.

[bdresser]

@p-s-dev thanks for the feedback - this was partially handled in #5096 by persisting the most recent three custom RPC URLs.

We will hopefully add more robust management features as we explore allowing users to add ETH-like networks or dapp-suggested custom RPCs.

Closing for this issue for now - I've flagged your feedback for our designer, and you can keep up on these proposed features on #5101 (comment) or #3604