[ZhuchkaTriplesix]

Closes #1432

Changes

1. Enable Extended JSON syntax highlighting:
   • Switched MongoDocumentsJsonView's controller instantiation in initState to SyntaxHighlightService.createHighlightController(language: QueryaCodeLanguage.json, text: ...).
   • The view now renders highlighted syntax rather than plain monochrome text.
2. Standard QueryaButton in toolbar:
   • "Copy JSON" action utilizes QueryaButton.secondary with QueryaControlSize.sm.
3. Unit tests:
   • Added widget test in test/features/mongodb/mongo_documents_view_modes_test.dart validating that MongoDocumentsJsonView uses QueryaHighlightController when syntax highlighting is initialized.