Add support for T5 family

[paucodeici]

Hi,

I like LMQL but i would like to use other model from huggingface than the one supported from AutoModelForCausalLM. Especially model from T5 family (like LaMini T5 ).

Does it make sense? (I didn't look yet what do they expose but it should be feasible?)

I am ok to propose a PR for this.

[lbeurerkellner]

PRs are very welcome :) I think it definitely makes sense, however, you have to handle the encoder/decoder separation of the input somehow.