Add dependency cooldowns (#1021)

This does two things:

- Bumps our Dependabot-side cooldowns to 30d
- Adds an NPM-side 7d cooldown

The idea is to give automated cooldowns a longer period, whereas humans
doing maintenance/manual bumps can opt into a newer package as needed.

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.github/dependabot.yml

@@ -5,11 +5,11 @@ updates:
     schedule:
       interval: daily
     cooldown:
-      default-days: 7
+      default-days: 30
 
   - package-ecosystem: npm
     directory: /
     schedule:
       interval: daily
     cooldown:
-      default-days: 7
+      default-days: 30

.npmrc

@@ -0,0 +1 @@
+min-release-age = 7