chore: Add Dependabot version-update cooldown (#407)

This pull request was auto generated by the LaunchDarkly Github
Standards automation platform.

* Ensure every entry under `updates` in `.github/dependabot.yml`
declares a cooldown of at least 7 days (default-days).
* Add entries for detected package ecosystems that were not yet tracked
by Dependabot.

Cooldown applies only to version updates; security updates bypass it, so
critical CVE fixes are never delayed.

Ref: SEC-8058.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Automation-only Dependabot policy change with no application runtime
or security-logic changes.
> 
> **Overview**
> Adds a **7-day cooldown** (`default-days: 7`) under both
**github-actions** and **npm** entries in `.github/dependabot.yml`, so
Dependabot still checks daily but waits before opening version-update
PRs for the same dependency.
> 
> Also normalizes minor YAML formatting on `updates:` and `schedule:`
(trailing whitespace). Security updates are unchanged and are not
subject to this cooldown.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
3950a63. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: ld-repository-standards[bot] <113625520+ld-repository-standards[bot]@users.noreply.github.com>

Author: ld-repository-standards[bot]

.github/dependabot.yml

@@ -1,10 +1,14 @@
 version: 2
-updates: 
+updates:
   - package-ecosystem: "github-actions"
     directory: "/"
-    schedule: 
+    schedule:
       interval: "daily"
+    cooldown:
+      default-days: 7
   - package-ecosystem: "npm"
     directory: "/"
-    schedule: 
+    schedule:
       interval: "daily"
+    cooldown:
+      default-days: 7