Flush out food product dating attributes

As discussed in #19, MIFC currently has food_expiration_date and needs `food_sell_by_date` for Food Data Central sample data. However, at least in the USA there are several dates associated with foods see this post from [USDA Food Safety Inspection Service](https://www.fsis.usda.gov/food-safety/safe-food-handling-and-preparation/food-safety-basics/food-product-dating) where they describe "Best if Used By/Before", "Sell-By", “Use-By", “Freeze-By” dates.

[This publication from UConn](https://publications.extension.uconn.edu/2019/10/30/expiration-use-by-and-sell-by-dates-what-do-they-really-mean/) describes more. I think more effort could be put into incorporating these as well as similar food packaging dates used in the USA as well as other countries. This would be a good first issue for anyone wanting to contribute to MIFC development.