metrics: Add TTFT/TPOT p95 dashboard

[tao12345666333]

Is your feature request related to a problem? Please describe.

#126 added support for TTFT/TPOT, but the Grafana dashboard26 added support for TTFT/TPOT, but the Grafana dashboard has not been updated yet

[Xunzhuo]

/area observability
/priority P1
/milestone v0.1

[tao12345666333]

/assign