Enable to set list of Networks through API

[igor-sirotin]

Description

For functional tests it's required to pass networks list with specific anvil URL.
With statusd it was done providing a node config directly, but with status-backend we should do this through some API.

Implementation

I found this:

status-go/protocol/requests/create_account.go

Line 69 in f660be0

TestOverrideNetworks []params.Network `json:"-"` // This is used for testing purposes only

Which I believe is ok to be used with status-backend. But there's an issue that on the next Login these networks are overwritten with defaults:
#5597 (comment) I tried to workaround this by passing same Networks to LoginAccount, but it didn't work out.