website: Add subcategories to docs for display on the Terraform Registry

[findkim]

We will soon be displaying documentation for this provider both on terraform.io and on the Terraform Registry.

Documentation displayed on the Terraform Registry will not use the ERB layout containing the existing navigation, and will instead build the navigation dynamically based on the directory and YAML frontmatter of a file. For providers that group similar resources and data sources by service or use case (subcategories), we'll need to add this information to the Markdown source file.

This PR modifies resource and data source documentation source files by adding a subcategory to the metadata if those files are currently grouped on terraform.io.

For more information about how documentation is rendered on the Terraform Registry, please see this reference: Terraform Registry - Provider Documentation.

[findkim]

Thanks @chrisst for moving these changes to the upstream docs! GoogleCloudPlatform/magic-modules#2585

I'll close this one out and open up one with just the docscheck CI changes.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. If you feel I made an error 🤖 🙉 , please reach out to my human friends 👉 [email protected]. Thanks!