Move snippets outside of markdown

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

docs/tests/core-concepts/client/plans/env.cue

@@ -0,0 +1,14 @@
+dagger.#Plan & {
+	client: env: {
+		REGISTRY_USER:  string
+		REGISTRY_TOKEN: dagger.#Secret
+	}
+
+	actions: pull: docker.#Pull & {
+		source: "registry.example.com/image"
+		auth: {
+			username: client.env.REGISTRY_USER
+			secret:   client.env.REGISTRY_TOKEN
+		}
+	}
+}