Add CMU Hinglish DoG Dataset for MT
Address part of #2841 

Added the CMU Hinglish DoG Dataset as in GLUECoS. Added it as a seperate dataset as unlike other tasks of GLUE CoS this can't be evaluated for a BERT like model. 
Consists of parallel dataset between Hinglish (Hindi-English) and English, can be used for Machine Translation between the two. 

The data processing part is inspired from the GLUECoS repo [here](https://github.com/microsoft/GLUECoS/blob/7fdc51653e37a32aee17505c47b7d1da364fa77e/Data/Preprocess_Scripts/preprocess_mt_en_hi.py)
The dummy data part is not working properly, it shows 
``` UnboundLocalError: local variable 'generator_splits' referenced before assignment ``` 
when I run without ``--auto_generate``.

Please let me know how I can fix that.
Thanks