Webpack: Fix channel format for loading status

[ndelangen]

Closes #23090

What I did

After using a Channel class to contruct the serverChannel, it now handled the wrapping and unwrapping of values between emit and subscribers.
The old code sending data from server wasn't changed and was wrapping the value needed to be sent over the channel in an array itself.

This caused the data to array in an unexpected format in the client, locking it into a ever-loading state,

How to test

1. Run a sandbox for template, e.g. yarn task --task sandbox --template cra/default-ts
2. Open Storybook in your browser

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[yannbf]

LGTM!