Add a cooldown to dependabot

This has become a recommended way to reduce the risk of supply chain attacks. 10 days is fairly arbitrary and could be shortened or lengthened in the future.

Author: zetter-rpf

.github/dependabot.yml

@@ -2,5 +2,7 @@ version: 2
 updates:
 - package-ecosystem: "bundler"
   directory: "/" # Location of package manifests
+  cooldown:
+    default-days: 10
   schedule:
     interval: "daily"