Forms: Add UI Builder repository PreValueSource example

[rickbutterfield]

📋 Description

Adds documentation for Forms v16 and v17 about configuring a PreValueSource based on a UI Builder Repository.

📎 Related Issues (if applicable)

N/A

✅ 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)

Forms 16.0.0 / UI Builder 16.1.1
Forms 17.0.0 / UI Builder 17.0.0

Deadline (if relevant)

November 27th 2025

📚 Helpful Resources

• 🧾 Umbraco Contribution Guidelines
• ✍️ Umbraco Documentation Style Guide

[eshanrnh]

Looks good 🙌 I've added a few suggestions to bold the UI terms and change user to "you".