Add custom bundlerURL to clientside preview

What does this MR do?

This MR adds an application setting for web_ide_clientside_preview_bundler_url and passes this to the codesandbox manager in the client. This enables GitLab to host this feature instead of reaching out to a third-party server.

• Relevant issue #27144 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• 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