equinix_metal_operating_system.provisionable_on shouldn't be a computed attribute?

[ocobles]

Now provisionable_on is defined as an argument used to filter by the desired plan. The problem with this approach is that the data source returns an error if it is not provisionable on that plan, and users also lose important information that the API returns, the full list of eligible plans. I think it will be better and more useful to match API behavoir and allow users to choose one of the eligible plans as they actually use the operating system as the primary requirement