Would be nice to be able to specify different input formats for each input to nds_validate.py

[jbrennan333]

I would like to be able to use nds_validate.py to compare two runs that used different output formats (e.g., parquet vs orc).
Currently there is only one --input_format parameter. Ideally, I would not have to specify this at all, and the tool would figure out what format the data files are. But in the absence of that, maybe provide an optional way to specify different formats for input1 and intput2.