server: improve add_warning method

Add an exc_info parameter that optionally takes an
exception that is passed to the logging function. This
will log the traceback without an additional logging call.

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

moonraker/components/button.py

@@ -31,7 +31,7 @@ class ButtonManager:
                 btn = GpioButton(cfg)
             except Exception as e:
                 msg = f"Failed to load button [{cfg.get_name()}]\n{e}"
-                self.server.add_warning(msg)
+                self.server.add_warning(msg, exc_info=e)
                 continue
             self.buttons[btn.name] = btn
         self.server.register_notification("button:button_event")