Tools to easily navigate await-tree

[kwannoel]

https://github.com/risingwavelabs/risingwave/issues/18176 can work in most cases.

But consider when the blocking duration is an hr. There can be no throughput or actor blocking duration metrics at all, and the graph in the dashboard will just be blank.

In such a scenario only await-tree / cpu flamegraph can tell us what's going on.

I still want some tools to quickly navigate the await-tree to tell us what's the blocking actor.

The await tree dump can be easily parsed and converted into a graph.