Add option to color flame graph by kernel/native/JIT/interpreter/inlined/user

I think it may be useful to have a coloring option that classify frames by something like kernel/native/JIT/interpreter/inlined/user, and possibly use name hash and hue for second-level classification.

For example, [Brendan Greg did this](https://www.brendangregg.com/blog/2017-07-30/coloring-flamegraphs-code-type.html), and also Java async-profiler (wrapped by pyroscope-java).

It seems to exist in explore mode but not app plugin.

I suggest to add a suitable legend, too.