add configurations for vitest

packages/slack/.eslintrc.js

@@ -0,0 +1,5 @@
+module.exports = {
+  extends: [
+    'plugin:vitest/recommended',
+  ],
+};

packages/slack/tsconfig.json

@@ -5,7 +5,10 @@
     "baseUrl": ".",
     "paths": {
       "~/*": ["./src/*"]
-    }
+    },
+    "types": [
+      "vitest/globals"
+    ]
   },
   "include": [
     "src"