Add changelog entry for Terraform v5.13.0

[musa-cf]

Summary

This is the changelog entry for the release of v5.13.0 for our Cloudflare Terraform provider.

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.

[KaydeeDee]

Updated to reflect CF TF Docs