Enhancement: allow users to select network during onboarding, in Onboarding v2

https://github.com/MetaMask/metamask-extension/issues/16696 importantly requests that we allow users to set a custom rpc during onboarding.

We should also allow users to select between our suggested networks during onboarding. This does not need to be resolved at the same time as the issue linked above, but can be.

We need to make it possible for the users to understand the implications of selecting different networks. Some of the providers are Infura, some are not.

Mobile version of https://github.com/MetaMask/metamask-extension/issues/16708

Read the linked issues #16696 and #16708 alongside the Onboarding v2 context first. Define the onboarding flow and user-facing explanation for choosing among suggested networks, including whether providers use Infura; done means users can select a suggested network and understand its implications.

Written by the indexing model from the issue text.