Merge 2 flamegraphs

First of all, thanks for maintaining this open-source project, I appreciate it.

When using Java SDK (based on async profiler), we have 2 profilings getting exposed, `memory-alloc_in_new_tlab_bytes` and `memory-alloc_outside_tlab_bytes`.

Unfortunately, the concept of tlabs might not be easy for everyone. In an ideal world, we want to expose 2 dashboards.
One with aggregated memory flamegraphs exposed, for more novice users, or to have a global view.
One with tlabs specific flamegraphs, for more advanced users.

Currently, this is not doable.

@simonswine pointed out [relabelling](https://github.com/grafana/pyroscope/pull/3369) which will be available in 1.7, which might solve our issue