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/set.cue

@@ -0,0 +1,25 @@
+package docker
+
+import (
+	"dagger.io/dagger"
+)
+
+// Change image config
+#Set: {
+	// The source image
+	input: #Image
+
+	// The image config to change
+	config: dagger.#ImageConfig
+
+	_set: dagger.#Set & {
+		"input":  input.config
+		"config": config
+	}
+
+	// Resulting image with the config changes
+	output: #Image & {
+		rootfs: input.rootfs
+		config: _set.output
+	}
+}