login button requires scope (User.Read)

[TheJoeFin]

Fixes #

The Login button requires User.Read scope to work. If it is not present confusing errors pop up.

Docs for Toolkit PR #

What changes to the docs does this PR provide?

Adds a small line to the LoginButton page which clarifies which scopes are required for this control to work.
Helps clarify Windows Provider, but not MSAL like in #593

PR Checklist

Please check if your PR fulfills the following requirements:

• Correctly picked the right branch to base the change off (dev for new features, master for typos/improvements)
• For new pages, used the provided template
• For new features, added an entry in the Table of Contents
• Ran against a spell and grammar checker
• Contains NO breaking changes

Other information

[opbld32]

Docs Build status updates of commit 4a24a65:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/graph/controls/LoginButton.md	✅Succeeded	View

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