Add template and template version management capability to coderd provider

[johnstcn]

Should cover use cases similar to the following:

resource "coderd_template" "debug" {
  display_name = "Debug template"
  description = "For use by admins only"
  allow_user_autostart = false
  allow_user_autostop = false 
  acl = {
    group {
      name = "template_admins"
      role = "use"
    }
    user {
      name = "someone_trusted"
      role = "admin"
    }
  }
  active_version_id = coderd_template_version.debug.id
}

resource "coderd_template_version" "debug" {
  name = data.git_branch.main.sha
  files = {
    "main.tf" = <<EOF
      [...]
    EOF
    "README.md" = <<EOF
      [...]
    EOF
  }
  
  tags = {
    name = "foo"
    value = "bar"
  }
}

resource "docker_image" "k8s_base" {
  name = "k8s_base"
  build {
    context = "."
    tag     = ["k8s_base"+git_repo.dev.main.sha]
  }
}
resource "coderd_template_version" "latest" {
  name = data.git_branch.main.sha
  files = {
	  "main.tf" = <<EOF
	    [...]
	    resource docker_container "dev_cont" {
	      image = "${docker_image.dev.name}"
	    }
	  EOF
	  "README.md" = <<EOF
	    [...]
	  EOF
	}
}