Grafana drilldown impl

[jiekun]

Describe Your Changes

This is for easier tracking of the progress and the related impl example.

Checklist

The following checks are mandatory:

• My change adheres to VictoriaMetrics contributing guidelines.
• My change adheres to VictoriaMetrics development goals.

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Summary by cubic

Adds Grafana Drilldown support for Tempo by implementing the metrics query_range API and translating TraceQL metrics (including compare) to LogsQL. Enables charts, compare views, and exemplars (clickable trace links) in Grafana Explore/Drilldown.

• New Features

  • Added /select/tempo/api/metrics/query_range endpoint with quicktemplate JSON response.
  • Translates TraceQL metrics to LogsQL: rate, count/min/max/avg/sum/histogram_over_time, quantile_over_time, by() grouping, and compare().
  • compare(): auto-discovers attributes, counts baseline vs selection per value, supports topN and an optional selection window; maps status codes to names; ranks attributes by divergence and returns per-value and total series.
  • Histogram: parses bucket JSON, converts vmrange to second-based labels; emits per-value and total series.
  • Exemplars: samples trace IDs across the time range, attaches them to series, snaps values to nearest samples, and includes trace/span IDs for Grafana links.
  • Field mapping between TraceQL and VT fields; converts samples to Tempo series; expanded tests for translator, parser, compare, and params.
  • Trace index stream now stores has_root_span; set during ingestion when parentSpanID == "" for fast root-span detection.

• Refactors

  • lib/traceql: added metrics pipes (rate, *_over_time, quantile, compare), hint pipe with(), Tempo-style by() without explicit |; exposed MetricsComponents, HasNonHintPipe, StripHintPipes.
  • Search APIs ignore hint pipes; return empty results for malformed filters; map nestedSetParent < 0 to root spans; map status names to OTEL codes.
  • Added request metrics for the new endpoint.

^{Written for commit fddd701. Summary will update on new commits.}