feat: Async api (#60)

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

docling_serve/engines/base_orchestrator.py

@@ -0,0 +1,21 @@
+from abc import ABC, abstractmethod
+
+from docling_serve.datamodel.engines import Task
+
+
+class BaseOrchestrator(ABC):
+    @abstractmethod
+    async def enqueue(self, task) -> Task:
+        pass
+
+    @abstractmethod
+    async def queue_size(self) -> int:
+        pass
+
+    @abstractmethod
+    async def task_status(self, task_id: str) -> Task:
+        pass
+
+    @abstractmethod
+    async def task_result(self, task_id: str):
+        pass