Replace existing plan should not create a new plan_uuid

🚧 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/replace-existing-plan-should-not-create-a-new-plan-uuid/
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The plan should hav a permalink, not get a new plan_uuid when saving updated routes, replacing exiting route.

Then We can link distribute a link that always will be updated based on the saved version.

Speaking of saved routes; It would be nice to make default save as replace the current route, and save as new route to be a choice.