[Inference] ADD async and sync Api server using FastAPI (#5396)

* add api server

* fix

* add

* add completion service and fix bug

* add generation config

* revise shardformer

* fix bugs

* add docstrings and fix some bugs

* fix bugs and add choices for prompt template

colossalai/inference/server/completion_service.py

@@ -0,0 +1,35 @@
+import asyncio
+
+from colossalai.inference.core.async_engine import AsyncInferenceEngine
+
+from .utils import id_generator
+
+
+class CompletionServing:
+    def __init__(self, engine: AsyncInferenceEngine, served_model: str):
+        self.engine = engine
+        self.served_model = served_model
+
+        try:
+            asyncio.get_running_loop()
+        except RuntimeError:
+            pass
+
+    async def create_completion(self, request, generation_config):
+        request_dict = await request.json()
+        request_id = id_generator()
+        prompt = request_dict.pop("prompt")
+
+        # it is not a intuitive way
+        self.engine.engine.generation_config = generation_config
+        result_generator = self.engine.generate(request_id, prompt=prompt)
+
+        final_res = None
+        async for res in result_generator:
+            if await request.is_disconnected():
+                # Abort the request if the client disconnects.
+                await self.engine.abort(request_id)
+                return {"error_msg": "Client disconnected"}
+            final_res = res
+
+        return final_res