Allow usage of custom for resource business_unit_company and business_unit_division

[gasttor]

Currently it is not possible to use custom for the resources commercetools_business_unit_company as well as commercetools_business_unit_division

Would it be possible to add it, so that that block like below can be used?

custom {
    type_id = commercetools_type.test.id
    fields = {
	"my-field" = "bar"
    }
}

[demeyerthom]

Hi @gasttor yeah that should not be a problem! I will see if I can free up some time to pick it up.

If you are in a hurry feel free to make a PR adding this feature, I am always happy to review it! We probably want to add something along the lines of commercetools/custom_fields.go, but as part of the internal namespace instead

[gasttor]

Hi @demeyerthom,
I can have a look at this. But to get familiar with the code I started with an easier fix. I just provided a PR for issue 522. Maybe we can start with this :)