Add Forms 13.6.0 and 16.1.0 release notes and update licensing model page

[ronaldbarendse]

📋 Description

This adds the release notes for Forms 13.6.0 and 16.1.0 and updates the licensing model pages with information and instructions on how to install the subscription-based license.

📎 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 13.6 and 16.1

Deadline (if relevant)

These versions will be released today, but the license changes are applicable from September 1st, 2025.

📚 Helpful Resources

• 🧾 Umbraco Contribution Guidelines
• ✍️ Umbraco Documentation Style Guide

[sofietoft]

Thanks for the PR @ronaldbarendse .

Please see my comments.
I've only reviewed version 13 so far.
Will review the remaining once you've checked the comments on version 13. Looks like mostly the same content has been added across versions.

[ronaldbarendse]

Thanks @sofietoft! I've applied the suggestions and updated the version 16 pages as well 💪🏻

[sofietoft]

Looks great @ronaldbarendse !

Thanks for considering my suggestions, and taking care of the other versions as well.

I'll get this merged 💪