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-pull/plan/pull.cue

@@ -0,0 +1,26 @@
+package docker
+
+import (
+	"dagger.io/docker"
+	"dagger.io/dagger/op"
+	"dagger.io/alpine"
+)
+
+ref: string @dagger(input)
+
+TestPull: {
+	pull: docker.#Pull & {from: ref}
+
+	check: #up: [
+		op.#Load & {from: alpine.#Image},
+		op.#Exec & {
+			always: true
+			args: [
+				"sh", "-c", """
+					 grep -q "test" /src/test.txt
+					""",
+			]
+			mount: "/src": from: pull
+		},
+	]
+}