Update MetaMask third-party docs

[alexandratran]

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Description

This PR updates the MetaMask Smart Accounts doc page with our rebranded package name, new documentation URLs, and a new section with a full step-by-step guide. The new URLs are not yet live in the MetaMask docs, so this PR should remain in draft until those are updated.

Fixes MetaMask/metamask-docs#2202

Document type

• Gentle introduction
• Quickstart
• How-to
• Concept
• FAQ
• Troubleshooting
• Reference
• Third-party content
• Not applicable

Checklist

• I have read the CONTRIBUTE.md guidelines
• My changes follow the style conventions outlined in CONTRIBUTE.md
• I have used sentence-case for titles and headers
• I have used descriptive link text (not "here" or "this")
• I have separated procedural from conceptual content where appropriate
• I have tested my changes locally with yarn start or yarn build
• My code follows the existing code style and conventions
• I have added/updated frontmatter for new documents
• I have checked for broken links
• I have verified that my changes don't break the build
• Third-party docs only: Do you agree to the third-party content policy outlined within CONTRIBUTE.md?
  • Yes
  • Not applicable

Additional Notes

[vercel]

@alexandratran is attempting to deploy a commit to the Offchain Labs - AF Billed Team on Vercel.

A member of the Team first needs to authorize it.