feat: extend inline metrics to ECS/ELB

[yimsk]

Follow-up from #32 / PR #45

Extend inline metrics sparkline support to additional resources.

Remaining Resources

ECS Services

• Challenge: Requires 2 dimensions (ClusterName + ServiceName)
• Metrics: CPUUtilization, MemoryUtilization
• Namespace: AWS/ECS

ELB (ALB/NLB)

• Challenge: Different namespaces for ALB vs NLB
• Metrics: RequestCount
• Namespace: AWS/ApplicationELB or AWS/NetworkELB

Implementation Notes

Current MetricSpec supports single dimension only:

type MetricSpec struct {
    Namespace     string
    MetricName    string
    DimensionName string  // Single dimension
    Stat          string
    ColumnHeader  string
}

ECS requires:

Dimensions: []types.Dimension{
    {Name: "ClusterName", Value: clusterName},
    {Name: "ServiceName", Value: serviceName},
}

Options

1. Extend MetricSpec to support multiple dimensions
2. Add DimensionBuilder func(resource dao.Resource) []types.Dimension

Additional Enhancements (Optional)

• Multiple metrics per resource (e.g., RDS: CPU + FreeableMemory)
• Lambda Errors metric alongside Invocations