plugin/framework: Initial State Upgrade information

[bflad]

What

• Created /plugin/framework/resources/state-upgrade page and add to plugin navigation
• Update /plugin/framework/resources for UpgradeState method
• Update /plugin/which-sdk page to remove missing feature

Why

Reference: hashicorp/terraform-plugin-framework#42
Reference: hashicorp/terraform-plugin-framework#292

The next release of terraform-plugin-framework will support provider defined managed resource state upgrades, which is a major missing feature for parity with SDKv2.

Screenshots

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Merge Checklist

If items do not apply to your changes, add (N/A) and mark them as complete.

Pull Request

• One or more labels describe the type of change (e.g. clarification) and associated product (e.g. tfc).
• Description links to related pull requests or issues, if any.

Content

• Redirects have been added for moved, renamed, or deleted pages.
• Sidebar navigation files have been updated for added, deleted, reordered, or renamed pages.
• Links to related content where appropriate (e.g., API endpoints, permissions, etc.).
• Pages with related content are updated and link to this content when appropriate.
• New pages have metadata (page name and description) at the top.
• New images are 2048 px wide. They have HashiCorp standard annotation color (#F92672) and format (rectangle with rounded corners), blurred sensitive details (e.g. credentials, usernames, user icons), and descriptive alt text in the markdown for accessibility.
• New code blocks have the correct syntax and line breaks to eliminate horizontal scroll bars.
• UI elements (button names, page names, etc.) are bolded.
• The Vercel website preview successfully deployed.

Reviews

• I or someone else reviewed the content for technical accuracy.
• I or someone else reviewed the content for typos, punctuation, spelling, and grammar.

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Name	Status	Preview	Updated
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[detro]

This goes well beyond the level of details I was expecting: it provides full examples for the cases where people provide previous schema and when they don't.

🎩

[bflad]

Will merge once this functionality is released. 👍