ci: bench: support sse and fix prompt processing time / server: add tokens usage in stream OAI response (#6495)

* ci: bench: support sse and fix prompt processing time
server: add tokens usage in stream mode

* ci: bench: README.md EOL

* ci: bench: remove total pp and tg as it is not accurate

* ci: bench: fix case when there is no token generated

* ci: bench: change to the 95 percentile for pp and tg as it is closer to what the server exports in metrics

* ci: bench: fix finish reason rate