Feature request — allow user to customize RPC URLs

[nik-suri]

Description and context

Public chain RPCs can be quite unreliable, especially on testnet. Currently, if the RPC that is hardcoded into the UI is down, the UI shows incorrect information and users cannot perform any actions. It would be really helpful to add an "advanced settings" context where the user can set a custom RPC URL to use.

Definition of done

Feature implemented and released.