Document how to integrate the anomaly chart to the dashboard

Goal

Requires !16530 (merged) to be merged. We should document what kind of yml should be added to the dashboard to make use of the anomaly charts.

Example that could work in the docs:

.gitlab/dashboards/custom_dashboard.yml

dashboard: 'My Dashboard'
panel_groups:
  - group: 'Memory Usage Variation'
    panels:
      - type: anomaly-chart
        title: "Anomalies Chart"
        y_label: "Pods"
        metrics:
          - id: cpu_usage_current
            query_range: avg(sum(rate(container_memory_usage_bytes[15m]))) /1024
            label: "Memory Usage Variation"
            unit: "KB" 
          - id: cpu_usage_upper
            query_range: 30000
            label: "Memory Usage Max"
            unit: "KB" 
          - id: cpu_usage_lower
            query_range: 5000
            label: "Memory Usage Min"
            unit: "KB"

Example (Using subqueries), not working yet:

Requires: #31279 (comment 229574331)

.gitlab/dashboards/custom_dashboard_2.yml

dashboard: 'My Dashboard'
panel_groups:
  - group: 'Memory Usage Variation'
    panels:
      - type: anomaly-chart
        title: "Anomalies Chart"
        y_label: "Pods"
        metrics:
          - id: cpu_usage_current
            query_range: avg(sum(rate(container_memory_usage_bytes[15m]))) /1024
            label: "Memory Usage Variation"
            unit: "KB" 
          - id: cpu_usage_upper
            query_range: (avg_over_time(rate(container_memory_usage_bytes[15m])[1w:15m]) + stddev_over_time(rate(container_memory_usage_bytes[15m])[1w:15m])) /1024
            label: "Memory Usage Max"
            unit: "KB" 
          - id: cpu_usage_lower
            query_range: (avg_over_time(rate(container_memory_usage_bytes[15m])[1w:15m]) - stddev_over_time(rate(container_memory_usage_bytes[15m])[1w:15m])) /1024
            label: "Memory Usage Min"
            unit: "KB"

!16530 (merged) should get merged first.