add gemma3 support

[BBC-Esq]

It'd be nice for ctranslate2 to have compatibility with at least one model that has vision model capabilities. since ct2 already supports gemma, it'd be a good opportunity to add one since gemma3 has a vision component:

see e.g.

google/gemma-3-12b-it

[maksimcialehin]

Yes, it will be nice if you add support of Gemma3 conversion. It has completely different architecture (due to multimodal), but the text part of the model is pretty similar to Gemma2.
Also Qwen3 models also appeared and they are waiting for CTranslate2 :)