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/push.cue

@@ -0,0 +1,32 @@
+package docker
+
+import (
+	"dagger.io/dagger"
+)
+
+// Upload an image to a remote repository
+#Push: {
+	// Destination ref
+	dest: #Ref
+
+	// Complete ref after pushing (including digest)
+	result: #Ref & _push.result
+
+	// Registry authentication
+	auth?: {
+		username: string
+		secret:   dagger.#Secret
+	}
+
+	// Image to push
+	image: #Image
+
+	_push: dagger.#Push & {
+		"dest": dest
+		if auth != _|_ {
+			"auth": auth
+		}
+		input:  image.rootfs
+		config: image.config
+	}
+}