[DOCS] Add deprecation notice to GitHub CLI Authentication

[deiga]

Resolves #3536

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Before the change?

• Unclear why gh CLI authentication doesn't work in new client

After the change?

• Adds deprecation notice to gh CLI authentication

Pull request checklist

• Schema migrations have been created if needed (example)
• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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[github-actions]

👋 Hi, and thank you for this contribution!

This repo is maintained by GitHub and community members on a best-effort basis. We'll get to this as soon as we can.

You can help us prioritize by joining the discussion on open issues and PRs, sharing details on the changes you need, and reviewing other contributions.

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[stevehipwell]

LGTM