Add ModernBERT to KerasHub

[gcuder]

ModernBERT has been released on HuggingFace. Since you can already load models from there into a Keras Backbone, it would be interesting to know, if this works as well.

https://huggingface.co/answerdotai/ModernBERT-base

[mattdangerw]

It does not yet work, as our Bert implementation does not support RoPE and alternating local/global attention.

Likely we would want to do this as a separate architecture (e.g. in a models/modern_bert/ directory), instead of sharing code with BERT, as its a substantially different architecture.

But we are planning to add it! It's a great fit for our library.

[gcuder]

Cool, let me know if I can help contributing to it.