Extension types: add PropertyEditorUi to Common Extension types list

[NguyenThuyLan]

📋 Description

• This PR updates the Common Extension Types documentation by adding the PropertyEditorUi entry.

• Introduced a short description of PropertyEditorUi and its purpose.

• Added a reference link to the official Umbraco documentation
  for further guidance.

📎 Related Issues (if applicable)

#7455

✅ Contributor Checklist

I've followed the Umbraco Documentation Style Guide and can confirm that:

• Code blocks are correctly formatted.
• Sentences are short and clear (preferably under 25 words).
• Passive voice and first-person language (“we”, “I”) are avoided.
• Relevant pages are linked.
• All links work and point to the correct resources.
• Screenshots or diagrams are included if useful.
• Any code examples or instructions have been tested.
• Typos, broken links, and broken images are fixed.

Product & Version (if relevant)

Deadline (if relevant)

📚 Helpful Resources

• 🧾 Umbraco Contribution Guidelines
• ✍️ Umbraco Documentation Style Guide