Slow down dependabot update frequency

Update dependabot to run weekly on a Monday.

Author: andycunningham-airelogic

.github/dependabot.yml

@@ -3,4 +3,8 @@ updates:
   - package-ecosystem: "nuget"
     directory: "/"
     schedule:
-      interval: "daily"
+      interval: "weekly"
+      day: "monday"
+    cooldown:
+      default-days: 3
+