Add export and load for dagger images

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

tests/tasks/export/export.cue

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"dagger.io/dagger"
+)
+
+dagger.#Plan & {
+	actions: test: {
+		image: dagger.#Pull & {
+			source: "alpine:3.15"
+		}
+
+		export: dagger.#Export & {
+			input:  image.output
+			config: image.config
+			tag:    "example"
+		}
+
+		verify: dagger.#Exec & {
+			input: image.output
+			mounts: exported: {
+				contents: export.output
+				dest:     "/src"
+			}
+			args: ["tar", "tf", "/src/image.tar", "manifest.json"]
+		}
+	}
+}