feat: add handling for missing source files in document processing

--bug=1062915 --user=刘瑞斌 【知识库】快速创建的文档，替换原文档报错，找不到源文件 https://www.tapd.cn/62980211/s/1789099

apps/knowledge/serializers/document.py

@@ -1538,8 +1538,15 @@ class DocumentSerializers(serializers.Serializer):
             source_file = QuerySet(File).filter(source_id=self.data.get('document_id')).first()
 
             if not source_file:
-                raise AppApiException(500, _('Source file not found'))
-
+                # 不存在手动关联一个文档
+                new_source_file = File(
+                    id=uuid.uuid7(),
+                    file_name=file.name,
+                    source_type=FileSourceType.DOCUMENT,
+                    source_id=self.data.get('document_id'),
+                )
+                new_source_file.save(file.read())
+            else:
                 # 获取原文件的sha256_hash
                 original_hash = source_file.sha256_hash