ci: Add Dependabot version-update cooldown (#553)

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**
> CI/automation-only change with no runtime code; only affects how and
when Dependabot opens dependency PRs.
> 
> **Overview**
> Introduces **`.github/dependabot.yml`** to turn on automated
dependency updates across the repo.
> 
> Each `updates` entry uses a **weekly** schedule and a
**`cooldown.default-days: 7`** so routine version bumps are spaced out.
Coverage includes **Docker** (`examples/proxy-validation-test`),
**GitHub Actions** (repo root), and **npm** for the listed `libs/*`
packages.
> 
> Per the PR intent, cooldown affects version updates only; **security
updates are not delayed**.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
2cc7edd. 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

@@ -0,0 +1,68 @@
+version: 2
+updates:
+  - package-ecosystem: "docker"
+    directory: "/examples/proxy-validation-test"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/client-sdk"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/common"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/internal"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/networking"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/server-sdk"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/server-sdk-dynamodb-source"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/server-sdk-otel"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/server-sdk-redis-source"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "npm"
+    directory: "/libs/server-sent-events"
+    schedule:
+      interval: "weekly"
+    cooldown:
+      default-days: 7