Thread-level support

Async-profiler can label samples by tid, and dump it in bottom of stack traces for non-jfr, or in meta table if jfr. I tried both:
1.
```
PYROSCOPE_AP_EXTRA_ARGUMENTS=jstackdepth=1024,threads
PYROSCOPE_PROFILER_EVENT=itimer
PYROSCOPE_FORMAT=jfr
```
2.
```
PYROSCOPE_AP_EXTRA_ARGUMENTS=jstackdepth=1024,threads
PYROSCOPE_PROFILER_EVENT=itimer
PYROSCOPE_FORMAT=collapsed
```

but it ends up in grafana cloud pyroscope app plugin without tid. I guess its server issue?

Start by reproducing the two configurations in the issue with PYROSCOPE_FORMAT set to jfr and collapsed, then compare the thread identifiers in the profiler output with their representation in the Grafana Cloud Pyroscope app. Done means thread-level identifiers are preserved and visible, or the responsible component is clearly identified.

Scritto dal modello di indicizzazione a partire dal testo della issue.