[example] add gemma model support with example.

[marvin-Yu]

1. add gemma model into example.cpp;
2. Verified the Gemma series models, including CodeGemma, Gemma1.1, and Gemma. Due to the same structure, all three models are supported, and they have been validated in examples and web demos. Currently, the test routines for these models are consistent with Gemma. https://huggingface.co/collections/google/codegemma-release-66152ac7b683e2667abdee11 https://huggingface.co/collections/google/gemma-release-65d5efbccdbb8c4202ec078b