Note that slug is required.

Per new task on [story 57529526](https://www.pivotaltracker.com/story/show/57529526); follow-up to [PR 569](https://github.com/reciprocity/ggrc-core/pull/569).

Since we don't yet have slug/code auto-generation, we are just marking these as required for now (behavior of import already treats them as such).