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/package.json

@@ -0,0 +1,11 @@
+{
+  "license": "Apache-2.0",
+  "scripts": {
+    "test": "bats --report-formatter junit --jobs 4 $(find . -type f -name '*.bats' -not -path '*/node_modules/*')"
+  },
+  "devDependencies": {
+    "bats": "^1.5.0",
+    "bats-assert": "^2.0.0",
+    "bats-support": "^0.3.0"
+  }
+}