server: continuous performance monitoring and PR comment (#6283)

* server: bench: init

* server: bench: reduce list of GPU nodes

* server: bench: fix graph, fix output artifact

* ci: bench: add mermaid in case of image cannot be uploaded

* ci: bench: more resilient, more metrics

* ci: bench: trigger build

* ci: bench: fix duration

* ci: bench: fix typo

* ci: bench: fix mermaid values, markdown generated

* typo on the step name

Co-authored-by: Xuan Son Nguyen <thichthat@gmail.com>

* ci: bench: trailing spaces

* ci: bench: move images in a details section

* ci: bench: reduce bullet point size

---------

Co-authored-by: Xuan Son Nguyen <thichthat@gmail.com>

examples/server/bench/prometheus.yml

@@ -0,0 +1,9 @@
+global:
+  scrape_interval:     10s
+  external_labels:
+    llamacpp: 'server'
+
+scrape_configs:
+  - job_name: 'llama.cpp server'
+    static_configs:
+      - targets: ['localhost:8080']