Adds logging of messageExceptions in the fastapi exception handler.

We're intentionally not doing a full log.exception with the traceback
here, though we could.  This exception will also be dispatched to Sentry
if configured, this just makes logs less opaque when one sees a 500.

lib/galaxy/webapps/base/api.py

@@ -1,3 +1,4 @@
+import logging
 import os
 import stat
 import typing
@@ -32,6 +33,9 @@
     )
 
 
+log = logging.getLogger(__name__)
+
+
 # Copied from https://github.com/tiangolo/fastapi/issues/1240#issuecomment-1055396884
 def _get_range_header(range_header: str, file_size: int) -> typing.Tuple[int, int]:
     def _invalid_range():
@@ -189,6 +193,10 @@ async def validate_exception_middleware(request: Request, exc: RequestValidation
 
     @app.exception_handler(MessageException)
     async def message_exception_middleware(request: Request, exc: MessageException) -> Response:
+        # Intentionally not logging traceback here as the full context will be
+        # dispatched to Sentry if configured.  This just makes logs less opaque
+        # when one sees a 500.
+        log.error(f"MessageException: {exc}")
         return get_error_response_for_request(request, exc)