Improve #docker.Push definition :

- Push to private registry
- Output ref and digest
- Update doc
- Add tests to universe.bats

Signed-off-by: Tom Chauveau <tom.chauveau@epitech.eu>

stdlib/.dagger/env/docker-push-invalid-creds/plan/push.cue

@@ -0,0 +1,34 @@
+package docker
+
+import (
+	"dagger.io/docker"
+	"dagger.io/random"
+)
+
+TestRegistry: {
+	username: string @dagger(input)
+	secret:   string @dagger(input)
+}
+
+TestPush: {
+	tag: random.#String & {seed: "docker push and pull should fail"}
+
+	name: "daggerio/ci-test:\(tag.out)"
+
+	image: docker.#ImageFromDockerfile & {
+		dockerfile: """
+				FROM alpine
+				RUN echo "test" > /test.txt
+			"""
+		context: ""
+	}
+
+	push: docker.#Push & {
+		"name": name
+		source: image
+		registry: {
+			username: TestRegistry.username
+			secret:   TestRegistry.secret
+		}
+	}
+}