[Doc] Changed explanation of generation_tokens_total and prompt_tokens_total counter type metrics to avoid confusion

[insukim1994]

FIX #16783 (link existing issues this PR will resolve)

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[markmc]

Thanks. The typo originates from the Grafana dashboard. It would be great to fix it there too:

• vllm/examples/online_serving/prometheus_grafana/grafana.json

  Line 307 in 11c3b98

  "legendFormat": "Generation Tokens/Sec",

• vllm/examples/online_serving/prometheus_grafana/grafana.json

  Line 290 in 11c3b98

  "legendFormat": "Prompt Tokens/Sec",

[insukim1994]

Thanks. The typo originates from the Grafana dashboard. It would be great to fix it there too:

• vllm/examples/online_serving/prometheus_grafana/grafana.json

  Line 307 in 11c3b98

  "legendFormat": "Generation Tokens/Sec",

• vllm/examples/online_serving/prometheus_grafana/grafana.json

  Line 290 in 11c3b98

  "legendFormat": "Prompt Tokens/Sec",

Sure! I will also fix them too. Thanks for double checking!

[insukim1994]

I tried to add @markmc's suggestion and I noticed that the legends at Grafana are correct since it is wrapped by rate() function:

• vllm/examples/online_serving/prometheus_grafana/grafana.json

  Line 302 in 11c3b98

  "expr": "rate(vllm:generation_tokens_total{model_name=\"$model_name\"}[$__rate_interval])",