Fix broken agent links in documentation

[kahirokunn]

What

This pull request updates all documentation links related to HCP Terraform agents to point to their new location in the terraform-docs-agents repository. The changes include updates to relative paths that were previously broken and have now been replaced with absolute URLs. Files updated include, but are not limited to:

• API documentation pages (e.g., api-docs/agents.mdx, api-docs/changelog.mdx)
• Integration guides (e.g., integrations/kubernetes/api-reference.mdx)
• Security and overview documentation
• Workspaces and dynamic provider credentials pages

Why

The HCP Terraform agent documentation has been migrated to a dedicated repository. As a result, existing links in our main documentation were no longer valid, causing broken navigation and potential confusion for users. By updating these links:

• Users are directed to the correct, up-to-date agent documentation.
• We ensure consistency and accuracy across our documentation.
• Overall user experience is improved by restoring full functionality of agent-related documentation.

Screenshots

N/A

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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. HCP Terraform).
• Description links to related pull requests or issues, if any.

Content

• Redirects have been added to website/redirects.js for moved, renamed, or deleted pages.
• API documentation and the API Changelog have been updated.
• 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.
• Sidebar navigation files have been updated for added, deleted, reordered, or renamed pages.
• 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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