ExpressionTool can be explicitly run under a CR
I'd like to explicitly see the output of an ExpressionTool under a container request. For example, I have an ExpressionTool that parses a directory and outputs only some of the files in a directory. I would like that output directory to be put in keep, but not saved under the final output. I was thinking there could be an arvados flag in an ExpressionTool that will create a container for the expression.