Add support for gemma models

[benglewis]

Hi 👋 ,

It would be really great if you could add support for the Gemma model series (i.e. 2B and 7B variants, particularly the 7B is what I would like most), since I see that it is currently not supported, but it is already supported by the mainstream transformers library.

[cszhz]

when will be gemma model supported?
thanks.