Add checks for ICE field offices 

Should add a check to make sure that we're only entering valid ICE field offices. Can set up similar to the other checks [here](https://github.com/uclalawcovid19behindbars/facility_data/blob/master/R/utilities.R#L276), and I think [this](https://www.ice.gov/contact/field-offices) should be set of codes. 