Add generation inference only

[SeanNaren]

🚀 Feature

Generation requires training via language modeling task, then is inference based. HF has a generation script to use LM head models or seq2seq models, we should offer a similar functionality, potentially with pipelines: https://github.com/huggingface/transformers/tree/master/examples/text-generation

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.