[Modular Transformers] Request for comments

[LysandreJik]

Hello 👋

Over the past few weeks, we've been merging PRs related to "Modular Transformers".

We explain why we chose to go that way in this tweet and this YouTube video at the PyTorch Conference by @ArthurZucker.

We detail how to use it, and have started putting in examples, in this documentation page. Finally, some models, like GLM, are being contributed (by @Cyrilvallez) using the modular file.

We'd be eager to hear about your experience using the tool. This is very much experimental, it is brittle, but we'll work on having it be more flexible, and usable in a myriad of situations. Please do share your experience (positive or negative), thoughts, comments, we'd be eager to hear what could be improved in order to lower even more the bar to contributing new models.