Improve PerfAggregator visualization

[SebastienGllmt]

Right now the perf metrics are saved to console. They're hard to really grasp because:

1. The format is kind of ugly
2. Some tasks run in parallel so it's hard to know what the bottleneck was

Probably we can:

1. Come up with a better way to visualize the perf in the console that maybe won't be great, but at least is better than what we have now
2. Come up with a more visual way to see the performance. Possibly we can modify the plan visualizer to also have an option to visualize past executions similar to this: https://github.com/sanpii/explain/tree/cte