Move APIKeys to file and allow read vs read/write

Helpers/ExtensionMethods.cs

@@ -0,0 +1,12 @@
+namespace TodoApi;
+
+public static class ExtensionMethods
+{
+    public static bool Contains(this IEnumerable<string> source, string toCheck, StringComparison comp)
+    {
+        return
+           source != null &&
+           !string.IsNullOrEmpty(toCheck) &&
+           source.Any(x => string.Compare(x, toCheck, comp) == 0);
+    }
+}