tests: Basic test infrastructure for Europa Universe

- Each package can include its own bats file (e.g. `universe.dagger.io/yarn/test/yarn.bats`)
- universe.dagger.io includes a common bash helper file
- bats is installed/launched through yarn with minimal setup
- shellcheck is done across the entire repo
- Integrated into our CI

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

pkg/universe.dagger.io/yarn/test/yarn.bats

@@ -0,0 +1,9 @@
+setup() {
+    load '../../bats_helpers'
+
+    common_setup
+}
+
+@test "yarn.#Build" {
+    dagger up ./yarn-test.cue
+}