Simplify connecting sync accounts when two exist

[graeme]

Task/Issue URL: https://app.asana.com/0/72649045549333/1208944782348823/f

Description:

Around 600 daily Sync users try to connect a Synced device with another Sync Backup, which is not possible, and we show them an error indicating they should stop syncing first and try again.

Simplify the steps by:

• Automatically Switch Sync for users with no other devices connected. (This is the most common scenario) -
• Ask, and allow them to continue switching sync for users with more devices connected.

Steps to test this PR:
https://app.asana.com/0/0/1208993297756834/f

also confirm that pixels are sent:
https://app.asana.com/0/1142021229838617/1208928557675008/f

Definition of Done:

• Does this PR satisfy our Definition of Done?

---

Internal references:

Pull Request Review Checklist
Software Engineering Expectations
Technical Design Template
Pull Request Documentation

[github-actions]

	Warnings
⚠️	PR has more than 500 lines of code changing. Consider splitting into smaller PRs if possible.

	Messages
📖	You seem to be updating localized strings. Make sure that you request translations and include translated strings before you ship your change. See Localization Guidelines for more information.

Generated by 🚫 dangerJS against 52a0d4e

[amddg44]

LGTM and really nice work on testing!

[github-actions]

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