fix(metric): filter out NaN due to divide by zero in Grafana

[hzxa21]

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What's changed and what's your intention?

We have many x / y pattern in the PromQL in grafana dashboard, which will show NaN noises when y == 0. This PR fixes the issue by adding > 0 or >= 0 in PromQL so that NaN will be filtered out.

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[hzxa21]

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