Add 7 day cooldown to Dependabot updates (#876)

Author: kelvin-chappell

.github/dependabot.yml

@@ -11,6 +11,8 @@ updates:
     groups:
       all:
         patterns: ["*"]
+    cooldown:
+      default-days: 7
 
   - package-ecosystem: "npm"
     directory: "/cdk"
@@ -29,3 +31,5 @@ updates:
     groups:
       all:
         patterns: ["*"]
+    cooldown:
+      default-days: 7