Add caching to month summary results

src/Solar.Api/Constants/CacheKeys.cs

@@ -0,0 +1,9 @@
+namespace Solar.Api.Constants;
+
+internal static class CacheKeys
+{
+    public static string GetMonthSummaryCacheKey(string source, int year, int month)
+    {
+        return $"month-summary-{source}-{year}-{month}";
+    }
+}