new call for model addition 
# What does this PR do?

This PR add a "call for model addition" to add [GLM](https://github.com/THUDM/GLM) model into the lib.
Think we still need to fill out a couple of things before publishing it :-) <|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.<|||||>unstale<|||||>@patil-suraj @patrickvonplaten 

I have started implementation of GLM model in HF. Need some input on implementation part.

1. Original GLM model is implemented using torch parallel distribution , In HF implementation, are we going to keep torch parallel distributed or convert to normal architecture(without parallelism )

2. There are six version of models (like GLM -base, GLM- large…etc), in which two diffrent tokenization is used  Wordpiece and BPE. Like GLM-base and large is having wordpiece and  'GLE-Roberta'and 'GLE-large' is having BPE.

