fix: UI project cannot handle fallback routes (feast-dev#3766)

* fix: fallback route cannot navigate to react page

Signed-off-by: snowron <snowronark@gmail.com>
Signed-off-by: Danny Chiao <danny@tecton.ai>

* refactor fix

Signed-off-by: snowron <snowronark@gmail.com>

---------

Signed-off-by: snowron <snowronark@gmail.com>
Signed-off-by: Danny Chiao <danny@tecton.ai>

sdk/python/feast/ui_server.py

@@ -77,7 +77,7 @@ def read_registry():
     # For all other paths (such as paths that would otherwise be handled by react router), pass to React
     @app.api_route("/p/{path_name:path}", methods=["GET"])
     def catch_all():
-        filename = ui_dir + "index.html"
+        filename = ui_dir.joinpath("index.html")
 
         with open(filename) as f:
             content = f.read()