cue modules: move stdlib to pkg/alpha.dagger.io

In preparation for Europa, we will vendor multiple CUE modules:

- `pkg/alpha.dagger.io`: legacy non-europa packages
- `pkg/dagger.io`: core Europa packages
- `pkg/universe.dagger.io`: Europa universe

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

pkg/alpha.dagger.io/docker/tests/command-host/command.cue

@@ -0,0 +1,13 @@
+package docker
+
+TestConfig: {
+	host: string @dagger(input)
+}
+
+TestHost: client: #Command & {
+	command: #"""
+			docker $CMD
+		"""#
+	host: TestConfig.host
+	env: CMD: "version"
+}