Add outputs.files task to plan

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

tests/plan/outputs/files/default_permissions.cue

@@ -0,0 +1,10 @@
+package main
+
+import "dagger.io/dagger"
+
+dagger.#Plan & {
+	outputs: files: test: {
+		contents: "foobar"
+		dest:     "./test"
+	}
+}

tests/plan/outputs/files/no_contents.cue

@@ -0,0 +1,7 @@
+package main
+
+import "dagger.io/dagger"
+
+dagger.#Plan & {
+	outputs: files: test: dest: "./test"
+}

tests/plan/outputs/files/usage.cue

@@ -0,0 +1,18 @@
+package main
+
+import "dagger.io/dagger"
+
+dagger.#Plan & {
+	outputs: files: {
+		[path=string]: dest: path
+		"test.sh": {
+			contents: """
+				#!/bin/bash
+				set -euo pipefail
+				echo "Hello World!"
+
+				"""
+			permissions: 0o750
+		}
+	}
+}