update action to dagger 0.2

- Remove AGE key setup
- Update README to use `dagger do`
- Update tests to dagger 0.2

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

test/cue.mod/pkg/universe.dagger.io/docker/image.cue

@@ -0,0 +1,23 @@
+package docker
+
+import (
+	"dagger.io/dagger"
+)
+
+// A container image
+#Image: {
+	// Root filesystem of the image.
+	rootfs: dagger.#FS
+
+	// Image config
+	config: dagger.#ImageConfig
+}
+
+// A ref is an address for a remote container image
+// Examples:
+//   - "index.docker.io/dagger"
+//   - "dagger"
+//   - "index.docker.io/dagger:latest"
+//   - "index.docker.io/dagger:latest@sha256:a89cb097693dd354de598d279c304a1c73ee550fbfff6d9ee515568e0c749cfe"
+// FIXME: add formatting constraints
+#Ref: dagger.#Ref