(#3446) Update GenerateDocs.ps1

The GenerateDocs.ps1 file has been modified to support the Astro
framework that docs.chocolatey.org will be using.

- Frontmatter keys are lowercase
- import the Xref Component
- Switch links to use the Xref Component
- Ensure all code is within code blocks and not 4 spaces
  (.mdx does not recognize code blocks as 4 spaces)
- Ensure NOTE and WARNINGS are formatted correctly
- Update comments to use `{/* stuff */}`  instead of `<!-- stuff -->`
- Change file format to `.mdx`