CMS: Adds new article on umbraco-extension

[iOvergaard]

Description

• Added a new guide, umbraco-extension-template.md, detailing how to use the umbraco-extension dotnet template to create and manage Umbraco extensions
• Updated Node.js version requirement from v20 to v22
• Merged the typescript-setup.md into development-flow/README.md for clarity and to avoid confusion

Minor Enhancements:

• Added a new redirect in .gitbook.yaml to point customizing/development-flow/typescript-setup to customizing/development-flow/README.md.
• Updated the vite-package-setup.md guide to reference the new Umbraco Extension Template as the recommended approach for building extensions.

Type of suggestion

• Typo/grammar fix
• Updated outdated content
• New content
• Updates related to a new version
• Other

Product & version (if relevant)

16.0.0

Deadline (if relevant)

ASAP

[Copilot]

Pull Request Overview

This PR introduces a new guide on using the umbraco-extension dotnet template to build Umbraco extensions, while also updating the Node.js version requirement and consolidating the TypeScript setup documentation into the main README.

• Added a detailed guide (umbraco-extension-template.md) for the Umbraco Extension Template.
• Updated Node.js version and related documentation to reflect LTS v22.15.0.
• Merged the TypeScript setup documentation from typescript-setup.md into README.md and added a corresponding redirect in .gitbook.yaml.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
16/umbraco-cms/customizing/development-flow/vite-package-setup.md	Updated info block with a link to the new extension template guide.
16/umbraco-cms/customizing/development-flow/umbraco-extension-template.md	New guide introducing the umbraco-extension dotnet template.
16/umbraco-cms/customizing/development-flow/typescript-setup.md	Removed as its content was merged into README.md.
16/umbraco-cms/customizing/development-flow/README.md	Merged TypeScript setup instructions and updated content and links.
16/umbraco-cms/.gitbook.yaml	Added a redirect for the removed typescript-setup.md file.

[eshanrnh]

Thanks for the PR, @iOvergaard 💪 We will review it as soon as we can 🙌

[leekelleher]

From a technical perspective, I am happy with the changes.

I have left a couple of suggestions, no showstoppers.

[eshanrnh]

Looks good to me, @iOvergaard I've added couple of suggestions to reduce the usage of "You" and change sentences to active voice - which I'll incorporate in a moment.