1st and 2nd grade Network preferences

🚧 THIS IS A TICKET MIGRATED FROM UPVOTY. The original ticket and comments will be available for a limited time over at:
https://abrp.upvoty.com/b/request-a-feature/1st-and-2nd-grade-network-preferences/
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I’d like so set Fastned as my main network but fall back to ionity when Fastned is not available along the route