Fix stale versioned docs links (#21630)

[ti-chi-bot]

This is an automated cherry-pick of #21630

This PR is translated from: pingcap/docs#22875

What changed

This PR updates stale documentation links reported in #22867:

• Moves versioned TiDB v7.2, v7.6, and v8.3 links to docs-archive.pingcap.com, preserving the original versioned targets.
• Updates the TiDB Cloud Starter TLS link to the current secure-connections-to-serverless-clusters page.
• Removes the broken TiDB roadmap hyperlink from the TiDB Cloud roadmap page because the linked docs page no longer exists in the current docs site.

Verification

• rg -n https://docs\\.pingcap\\.com/tidb/v(7\\.2|7\\.6|8\\.3)/|https://docs\\.pingcap\\.com/tidbcloud/secure-connections-to-starter-clusters/|https://docs\\.pingcap\\.com/tidb/dev/tidb-roadmap -g *.md returns no matches.
• Checked each new external URL introduced in the diff with Invoke-WebRequest; all returned HTTP 200.
• git diff --check
• npx --yes markdownlint-cli@0.17.0 <changed files>

[qiancai]

/approve

[ti-chi-bot]

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