added API routers for locations

app/api/available-years/route.ts

@@ -0,0 +1,9 @@
+import { fetchAvailableYears } from '@/app/lib/actions/monthActions';
+import { NextResponse } from 'next/server';
+ 
+export async function GET(request: Request) {
+
+  const availableYears = await fetchAvailableYears();
+
+  return NextResponse.json({ availableYears });
+}