Add spec code generation for spark client

### Is your feature request related to a problem? Please describe.

Today the request and response class are manually added to satisfy the special requirement for spark client usage with iceberg RestClient, where imports of iceberg shaded jar are needed.

Instead of adding it manually, we can add a generation script to auto generate it based on speck

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_