What problem does this address?

Extend the media REST API to provide client-side processing configuration including available image sizes, quality settings, and feature flags. In the current media experiment, these are passed as editor settings, this needs to be switched to the rest api.

See this comment: #64278 (comment)

Acceptance Criteria:

• Image sizes configuration exposed in REST API
• Big image threshold value available in REST API
• Supported mime types list provided in REST API
• Output format mapping preferences included in REST API
• All client side media configuration data loaded from REST API instead of editor settings.