Add Grafana dashboards to show failure signatures

Problem Statement

Once failure signatures are available in ClickHouse, we need dashboards to visualize and monitor signature patterns, trends, and quality metrics. This will help identify issues with signature generation and provide insights for improving the system.

Goal

Create Grafana dashboards to display failure signature analytics, including top signatures overall, highest diversity categories, and trending failure patterns.

Acceptance Criteria

• Create dashboard showing top X failure signatures overall
• Add dashboard for categories with highest diversity ratios
• Include trending failure patterns over time

Technical Approach

• Build dashboards on top of ClickHouse data from issue #293 (closed)
• Include filters for time ranges, projects, and specific categories
• Display both signature counts and diversity quality metrics

Dependencies

• Requires issue #293 (closed) (ClickHouse data pipeline) to be completed first

Related Work

Builds on gitlab-org/quality/triage-ops!3654 (merged)