Add support for HTTP proxying.

[seanparsons]

WHY are these changes introduced?

The node fetch function doesn't currently handle HTTP proxies and as a result if a user has a mandatory proxying requirement in their environment the upgrade check fails.

WHAT is this pull request doing?

In getChangelog, the regular fetch function has been switched out for the implementation provided by @shopify/cli-kit which does handle HTTP proxies correctly.

HOW to test your changes?

Running npx shopify hydrogen dev with this installed should result in the changelog being pulled if not in the monorepo.

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[github-actions]

We detected some changes in packages/*/package.json or packages/*/src, and there are no updates in the .changeset.
If the changes are user-facing and should cause a version bump, run npm run changeset add to track your changes and include them in the next release CHANGELOG.
If you are making simple updates to examples or documentation, you do not need to add a changeset.

[shopify]

Oxygen deployed a preview of your refactor/use-cli-kit-fetch branch. Details:

Storefront	Status	Preview link	Deployment details	Last update (UTC)
metaobjects	✅ Successful (Logs)	Preview deployment	Inspect deployment	March 28, 202511:27 AM
Skeleton (skeleton.hydrogen.shop)	❌ Error (Logs)	-	Inspect deployment	March 28, 2025 2:47 PM
custom-cart-method	❌ Error (Logs)	-	Inspect deployment	March 28, 2025 2:47 PM
classic-remix	✅ Successful (Logs)	Preview deployment	Inspect deployment	March 28, 202511:27 AM
third-party-queries-caching	❌ Error (Logs)	-	Inspect deployment	March 28, 2025 2:47 PM

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