spark: add word counter utility with tests

wizard-work/spark/sample_array.json

@@ -0,0 +1,5 @@
+[
+  {"id": 1, "name": "Alice", "active": true},
+  {"id": 2, "name": "Bob", "active": false},
+  {"id": 3, "name": "Charlie", "active": null}
+]