chore: add .lintstagedrc.json to kleros-app workspace for linting

Author: kyrers

kleros-app/.lintstagedrc.json

@@ -0,0 +1,6 @@
+{
+  "*.{js,jsx,ts,tsx}": [
+    "eslint --fix --no-error-on-unmatched-pattern",
+    "prettier --write --no-error-on-unmatched-pattern"
+  ]
+}