WIP: Feature / Mechanism to update network(s) config externally

[superKalo]

Tweaks for the predefined networks logic so that a new build is NOT needed when adding new network or changing an existing predefined network config. Moreover:

• Separate predefined networks, custom networks, and user network preferences
• Mechanism to override network config

Problems TODO solving:

• Once a custom network is added, there's no mechanism to update the network-status-related config (pulled from the RPC). The only workaround for the user is to remove and add again the custom network. So figure out a sensible approach to regularly update those instead. Example: Imagine a custom network where areContractsDeployed was initially false, but then, someone deployed the contracts.

TODO:

• Take the icons for all networks from the iconUrls (currently, for predefined networks, it's hardcoded)
• Take the bundler API key from Relayer's network config (currently, they're in the .env file)

Relayer part coming in https://github.com/AmbireTech/relayer/pull/1037

Part of https://github.com/AmbireTech/ambire-app/issues/3840