This adds support for using the Docker example on WIndows, as long as Docker is installed, of course. Works for both WSL and Hyper-V versions of Docker Desktop.

See: hashicorp/terraform-provider-docker#180 (comment).

Alternatives:

• Use a Terraform exec hack to detect the OS automatically
  • Downside: added complexity to template, less clear what behavior is
• Expose Coder deployment information as a Terraform data source #1879 (no steps required for Docker provider)

Closes #1789