Modernize docs and update GitHub Actions

[adambarreiro]

This PR transforms the old-style documentation for Terraform providers to the new one.

• Used https://github.com/hashicorp/terraform-provider-scaffolding-framework/tree/main/docs as reference
• Used https://github.com/hashicorp/terraform-plugin-docs tool to verify the structure and metadata from top of the files
• Used https://registry.terraform.io/tools/doc-preview tool to see that they render correctly after the changes

Tests and GH Actions are also updated accordingly.

[Didainius]

Thanks, 🤞🏻

[tenthirtyam]

Consider adding "Resource: " or "Datasource: " before each H1 header to ensure that the reader understands the context if landing on the page without using the navigation.

For example:

# Data Source: vcfa_content_library_item

# Resource: vcfa_content_library_item

[tenthirtyam]

11 instances of vcfa\_ still exist in the ./docs/resources path within the markdown H1s.

[lvirbalas]

Thank you!