text: Title: Qwen2 MoE manual `head_dim`
  Body: ### Feature request
  
  https://github.com/huggingface/transformers/blob/81aa9b2e07b359cd3555c118010fd9f26c601e54/src/transformers/models/qwen2_moe/modeling_qwen2_moe.py#L317
  
  For qwen2 moe, `head_dim` is now forced to be `hidden_size // num_heads`. 
  
  ### Motivation
  
  manual `head_dim` setting support in llama, mistal, mixtral modeling
  
  ### Your contribution
  
  PR