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/bats/tests/testfile/test.bats

@@ -0,0 +1,12 @@
+setup() {
+    load 'mods/bats-support/load'
+    load 'mods/bats-assert/load'
+}
+
+@test "simple bats test" {
+    run echo "Hello world"
+    assert_success
+
+    run cat /do/not/exist
+    assert_failure
+}