html and js for monthly budget summary

app/static/monthly_budget_summary.js

@@ -0,0 +1,10 @@
+const monthSelector = document.getElementById('month-selector');
+const tableBody = document.getElementById('table-body');
+
+
+document.addEventListener("DOMContentLoaded", (event) => {
+    displayMonthLineItems(monthSelector.value);
+    monthSelector.addEventListener('change', (e) => {
+        displayMonthLineItems(e.target.value);
+    })
+  });