Ensure reopt can only be run with reopt files & data

[vtnate]

Is your feature request related to a problem? Please describe.
It's possible to reopt post-process when you haven't run with reopt, which leads to inaccurate results

Describe the solution you'd like
Gracefully ensure reopt runs with the proper information.

Additional context
Zahra ran into this issue

[vtnate]

The run command doesn't use reopt, though the reopt post-processor needs the extra column in the scenario file to determine the correct assumptions file for each feature. We can simplify (eliminate 2 cli options, eliminate reopt_scenario_file) at the process command by:

1. copying the example assumptions files when the user requests a reopt post-processing
2. adding the assumptions file column to the existing scenario_file instead of making a new scenario_file