server : forward llama.cpp sampling params on /v1/messages (#30856)
* server : forward llama.cpp sampling params on /v1/messages
* server : pass the request through on /v1/messages instead of copying listed keys
* NIT: Change comment from multiline to single line
* server : accept llama.cpp params under extra_params on /v1/messages
* server : remove test case for trivial functionality
* server : show extra_params in the /v1/messages README example