Run pages configuration update in a worker

What does this MR do?

As a step in making web-workers not depend on NFS, this moves the pages configuration update out of the request into a worker.

If an exception occurs within the configuration update, the exception will now be returned from the service, and raised in the worker so it can be retried by Sidekiq.

Part of #230695 (closed)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry: Still behind a feature flag
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done