Fix median functions in visualizations in GCP GKE dashboard

[kaiyan-sheng]

Proposed commit message

This PR fixes visualizations that incorrectly used median on counter metrics, which produces meaningless results and triggers Kibana warnings. Replaced with appropriate operations for counter metrics.

Problem

Warnings about meaningless median operations on gcp.gke.node.network.received_bytes.count, gcp.gke.node.network.sent_bytes.count, gcp.gke.container.restart.count, and CPU usage counter metrics
Some visualizations showing empty data due to incorrect aggregations

Solution

For Time Series (Counter Metrics):

• Changed: median → differences operation (with max reference)
• Calculates the rate of change between consecutive time buckets

For Single-Value/Aggregations (Counter Metrics):

• Changed: median → last_value operation
• Shows the most recent cumulative count

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

Screenshots

Before:

After:

[elastic-vault-github-plugin-prod]

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[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: aacad5a

History

• 💔 Build #36236 failed 00db950
• 💔 Build #36235 failed 3cf0725
• 💚 Build #36201 succeeded 4aa162a

[kaiyan-sheng]

Please see https://github.com/elastic/beats/blob/main/x-pack/metricbeat/module/gcp/metrics/response_parser.go#L131-L132 for reference.

[elastic-vault-github-plugin-prod]

Package gcp - 2.47.1 containing this change is available at https://epr.elastic.co/package/gcp/2.47.1/