docs(node): add mTLS examples to TLS page

[Aryex]

Summary

Adds Node.js code examples for all four mTLS subsections on the Configure TLS page, replacing the "Coming soon" placeholders.

⚠️ Attention: This PR was generated automatically. Verify that all relevant pages have been updated.

Source Commits

• 4f74de2 — feat(node): add mTLS client certificate/key support with automatic certificate reloading (#6383)

Changes

• Replaced Node.js "Coming soon" placeholders in the mTLS section with complete code examples:
  • In-memory PEM (static) — kind: "bytes" with certBytes / keyBytes
  • Path-based with automatic reload — kind: "path" with certPath / keyPath
  • Path-based with custom reload interval — reloadIntervalSeconds: 60
  • Loading PEM material from files — loadClientCertificateAndKeyFromFile helper
• Extended the Common Pitfalls section with Node.js-specific notes (empty bytes rejection, uint32 interval validation)

Context

Node.js mTLS support (both byte-based via discriminated union and path-based with automatic reload) shipped in valkey-glide #6383. This extends the same feature previously landed for Java (#6386), Go (#6384), and Python (#6596). The existing doc PR #271 covers Java only and is authored from a fork; PR #304 covers Python. This PR adds the Node.js examples independently.

cc @xShinnRyuu

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This PR was generated by the automated documentation pipeline.