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/nginx/nginx.cue

@@ -0,0 +1,26 @@
+// Run and deploy the Nginx web server
+// https://nginx.org
+package nginx
+
+import (
+	"universe.dagger.io/docker"
+)
+
+// Build a nginx container image
+// FIXME: bootstrapping by wrapping "docker pull nginx"
+//    Possible ways to improve:
+//    1. "docker build" the docker hub image ourselves: https://github.com/nginxinc/docker-nginx
+//    2. Reimplement same docker build in pure Cue (no more Dockerfile)
+// FIXME: build from source or package distro, instead of docker pull
+#Build: {
+	output: docker.#Image & _pull.image
+
+	_pull: docker.#Pull
+	*{
+		flavor: "alpine"
+		_pull: source: "index.docker.io/nginx:stable-alpine"
+	} | {
+		flavor: "debian"
+		_pull: source: "index.docker.io/nginx:stable"
+	}
+}