feat: add in-reply-to and references to reply emails

[jmrobles]

Summary

Describe what the PR does and how to test. Photos and videos are recommended.

Add the option fields "In-Reply-To" and "References" for reply emails with "Send Email" node.

Related tickets and issues

Include links to Linear ticket or Github issue or Community forum post. Important in order to close automatically and provide context to reviewers.

https://community.n8n.io/t/add-in-reply-to-header-on-send-email-smtp-node/26962

Review / Merge checklist

• PR title and summary are descriptive. Remember, the title automatically goes into the changelog. Use (no-changelog) otherwise. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.

  A bug is not considered fixed, unless a test is added to prevent it from happening again.
  A feature is not complete without tests.

[CLAassistant]

All committers have signed the CLA.

[jmrobles]

how can we unblock this?