Add session attr to Bunch to facilitate app.model.session

This Bunch object already has `context`; however we access the session
using both attrs.

lib/galaxy/tools/remote_tool_eval.py

@@ -59,7 +59,8 @@ def __init__(
         tool_data_table_manager: ToolDataTableManager,
         file_sources: ConfiguredFileSources,
     ):
-        self.model = Bunch(context=sa_session)
+        # For backward compatibility we need both context and session attributes that point to sa_session.
+        self.model = Bunch(context=sa_session, session=sa_session)
         self.config = tool_app_config
         self.datatypes_registry = datatypes_registry
         self.object_store = object_store