Allow modifying the system default price sets or configure to have none attached at all.
On some clouds, there is a default Price Set that is attached to a Plan when it is synced from the source system. An example would be in OpenStack, there is a system Price Set called “Custom OpenStack Price Set”, which is attached to any Plans (flavors). It is requested to allow a different Price Set to be chosen as the default for a Plan sync’d or disable having a default attached at all initially. The idea of a default Price Set is useful but some configuration around it would be helpful.