server : refactor middleware and /health endpoint (#9056)
* server : refactor middleware and /health endpoint
* move "fail_on_no_slot" to /slots
* Update examples/server/server.cpp
Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
* fix server tests
* fix CI
* update server docs
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
