Feature Request: Add --aggregate-by option to Hubble CLI for flow data aggregation.

[bearslyricattack]

Currently, Hubble CLI provides excellent filtering capabilities but lacks the ability to aggregate flow data based on common fields. When monitoring network traffic in a busy Kubernetes cluster, it's often necessary to get a summarized view of traffic patterns rather than individual flows.

For example, I want to see how many connections exist between different pods and on which ports, rather than seeing each individual packet. This would be particularly useful for:

Identifying the most common traffic patterns
Detecting unusual communication between services
Troubleshooting connectivity issues
Visualizing application dependencies