Add enumeration for plant/grain specific proccess for debranning

For grains like barley and sorghum MIFC will need an enumeration to capture these plant or grain specific processes such debranning (referred to as pearled).

Similar examples may include de-husking however, that is typically needed to make grains edible, so perhaps not as relevant to include in MIFC?

No files, tests, or entry points are identified. Start by locating the existing MIFC process enumerations, then resolve the scope of debranning or pearling and possible de-husking entries; done means the agreed plant- or grain-specific process enumeration is documented consistently.

Written by the indexing model from the issue text.