Added Breaking change note and updated Custom error page article

[eshanrnh]

📋 Description

Added a note about the breaking change and the version in which the fix was introduced. I also tested the article and made the necessary updates to ensure it works correctly.

📎 Related Issues (if applicable)

Fixes #7258

✅ 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)

CMS V16.

Deadline (if relevant)

Anytime

📚 Helpful Resources

• 🧾 Umbraco Contribution Guidelines
• ✍️ Umbraco Documentation Style Guide

[eshanrnh]

I'm not sure why it is throwing the write short sentences error, as the sentences are less than 25 words 🤷‍♀️

[sofietoft]

Just one small suggestion. Otherwise the changes look great.