feat(core) Add CreateUser method to ExternalAuthenticationService Helper Class

[arrrrny]

Description

add createUser method to external authentication helper to support the case where user is authenticated
via external provider without email. There is a case (ie mobile app only store) where we only want authenticated users to see products and and be able to add to carts. This is also useful for anti-scraping.

I also returned savedUser from all methods for consistency and added type for missing method.

Breaking changes

Nope

Screenshots

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Checklist

📌 Always:

• I have set a clear title
• My PR is small and contains a single feature
• I have checked my own PR

I added description to the method

👍 Most of the time:

• I have added or updated test cases
• I have updated the README if needed

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Name	Status	Preview	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview	Aug 1, 2024 6:12am

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[arrrrny]

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[arrrrny]

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