Write function to check format of satellite data

[hannahnesser]

• Require that all needed fields are in the data (a model for this can be seen in read_satellite_file)
• Require that DATE is datetime64 (so we can access it as .dt.)
• Require that all levels be defined from bottom of atmosphere (not sure the best way of enforcing this--maybe check that pressure is monotonically decreasing? If not, reverse all level-defined variables?)