Added documentation for managing DOTNET_ENVIRONMENT

[ozgey99]

📋 Description

This PR adds documentation about the new section on Cloud Portal that lets users manage the DOTNET_ENVIRONMENT environment variable for their Umbraco Cloud Environment.

📎 Related Issues (if applicable)

✅ 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)

Umbraco Cloud

Deadline (if relevant)

No deadline 😄

📚 Helpful Resources

• 🧾 Umbraco Contribution Guidelines
• ✍️ Umbraco Documentation Style Guide

[eshanrnh]

The PR looks great, @ozgey99 🙌 I have added a few suggestions to add formatting to UI elements/names and a blank line between images.

[eshanrnh]

@ozgey99 After merging Bjarke's PR, there are some merge conflicts in this PR. Can you resolve them, please?

[eshanrnh]

Looks good to me, @ozgey99 💪