Consider loading the system by default in `get_decision_problem_results`

[GabrielKS]

Very minor interface change: a while ago, we added to the get_decision_problem_results a keyword argument to populate the system:

uc = get_decision_problem_results(results, "UC"; populate_system = true)

. We made it default to false for backwards compatibility, but a few times now I've fielded questions from people who forget to attach the system and then wonder why their analytics aren't working. Now that we serialize the system to the HDF5 container so it is always present, I propose we make populate_system default to true in the next breaking release. We can keep the option to opt out for special cases.

[jd-lara]

agree you can open a PR with this