- Introduced a new `docType` field in the `UpdateKnowledgeDocumentInput` to manage document type changes.
- Updated the `doUpdate` method to clear subtype fields (GuideType, AnswerType, CodeLang) when the document type changes.
- Added comprehensive tests for various document type transitions to ensure correct behavior and state preservation.
- Updated GraphQL schema and generated models to accommodate the new `docType` field.