[D1] Document US jurisdiction

[ivoryibu]

Summary

Adds a draft changelog entry and updates D1 data location documentation for the new US jurisdiction.

• Adds a hidden changelog entry with a Wrangler example so the announcement remains unpublished pending review.
• Adds us to the supported jurisdictions table so the location reference matches the available option.

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.