llama, server: add /v1/systemone API (models: laya, julia-1, lev, openjev, kev) (#29818)

* init conversion

* convert: ok

* model loaded

* add server code

* improve conversion script

* support shared prompt prefix

* add docs, imorove UX a bit

* add vision support

* add openjev tiny model for testing

* add dev docs

* support lev & kev

* clean up

* fix lev noul

* fix py lint

* nits docs

* clarify about not supporting date_facts