Optional parameters for operators

[rohitkulshreshtha]

I am adding an optional parameter to state_by to change how the lattice is constructed for load testing.

Some longer-term questions that need answers:

• Should we even support optional parameters?
• What if there are multiple optional parameters? That would imply some type of keyword arguments like say Python.

For now, I am just doing one optional parameter to unblock myself. It is impossible to do optional arguments since num_args is not a range, so I am unblocking myself with a mandatory argument.