Add upload_endpoint_path into flet.fastapi.app (flet-dev#2954)

* Update app.py

* Add description for upload_endpoint_path

sdk/python/packages/flet/src/flet/fastapi/app.py

@@ -3,6 +3,9 @@
 from typing import Awaitable, Callable, Optional, Union
 
 from fastapi import Request, WebSocket
+from flet_core.page import Page
+from flet_core.types import WebRenderer
+
 from flet.fastapi.flet_app import (
     DEFAULT_FLET_OAUTH_STATE_TIMEOUT,
     DEFAULT_FLET_SESSION_TIMEOUT,
@@ -12,8 +15,6 @@
 from flet.fastapi.flet_oauth import FletOAuth
 from flet.fastapi.flet_static_files import FletStaticFiles
 from flet.fastapi.flet_upload import FletUpload
-from flet_core.page import Page
-from flet_core.types import WebRenderer
 
 
 def app(
@@ -27,6 +28,7 @@ def app(
     use_color_emoji: bool = False,
     route_url_strategy: str = "path",
     upload_dir: Optional[str] = None,
+    upload_endpoint_path: Optional[str] = None,
     max_upload_size: Optional[int] = None,
     secret_key: Optional[str] = None,
     session_timeout_seconds: int = DEFAULT_FLET_SESSION_TIMEOUT,
@@ -46,6 +48,7 @@ def app(
     * `use_color_emoji` (bool) - whether to load a font with color emoji. Default is `False`.
     * `route_url_strategy` (str) - routing URL strategy: `path` (default) or `hash`.
     * `upload_dir` (str) - an absolute path to a directory with uploaded files.
+    * `upload_endpoint_path` (str, optional) - absolute URL of upload endpoint, e.g. `/upload`.
     * `max_upload_size` (str, int) - maximum size of a single upload, bytes. Unlimited if `None`.
     * `secret_key` (str, optional) - secret key to sign and verify upload requests.
     * `session_timeout_seconds` (int, optional)- session lifetime, in seconds, after user disconnected.
@@ -82,15 +85,16 @@ async def app_handler(websocket: WebSocket):
             session_handler,
             session_timeout_seconds=session_timeout_seconds,
             oauth_state_timeout_seconds=oauth_state_timeout_seconds,
+            upload_endpoint_path=upload_endpoint_path,
             secret_key=secret_key,
         ).handle(websocket)
 
     if upload_dir:
 
-        @fastapi_app.put(f"/{upload_endpoint}")
+        @fastapi_app.put(
+            f"/{upload_endpoint_path if upload_endpoint_path else upload_endpoint}"
+        )
         async def upload_handler(request: Request):
-            if not upload_dir:
-                return
             await FletUpload(
                 upload_dir=upload_dir,
                 max_upload_size=max_upload_size,