fix: qps float value precision

[luohoufu]

What does this PR do

This pull request includes an important change to the QueryQPS function in the modules/elastic/api/v1/cluster_overview.go file. The change improves the precision of the QPS calculations by using the util.ToFixed function to round the results to two decimal places.

Precision improvement in QPS calculations:

• modules/elastic/api/v1/cluster_overview.go: Modified the QueryQPS function to use util.ToFixed for rounding index, query, and index_bytes rates to two decimal places.

Rationale for this change

Standards checklist

• The PR title is descriptive
• The commit messages are semantic
• Necessary tests are added
• Updated the release notes
• Necessary documents have been added if this is a new feature
• Performance tests checked, no obvious performance degradation

[Copilot]

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modules/elastic/api/v1/cluster_overview.go:830

• Consider adding unit tests that explicitly verify the precision of the rounded QPS values to ensure that util.ToFixed behaves as expected in this context.

indexQPS[k]["index"] = util.ToFixed(maxIndexRate/float64(bucketSizeInSeconds), 2)