add Ellipsis (...) to compose

[bashirmindee]

Is your feature request related to a problem? Please describe.
I would like for the compose method to support ... which means the user wants the compose function to fill the rest all on its own. For example my_dag.compose(["node1"], [...]) means that the user wants to make a dag that takes as input the result of node1 and returns all outputs of the dag in the order already specified. Notice that tawazi must verify that the dag still returns all the ExecNodes it used to run in this case otherwise the order can not be garanteed.