`profilegen` script for generating synthetic profiling data

#### Is your feature request related to a problem? Please describe.

Hello! My team and I from Canonical are working on Charmed Pyroscope, a [Juju](https://canonical.com/juju/docs)-based distribution of Pyroscope maintained to automate deployment and day n operation on Pyroscope.

While testing OTLP profile ingestion into Charmed Pyroscope, we ran into the problem that there is currently no easy way to automatically generate profiling data and verify that it is being correctly ingested by Pyroscope.

#### Describe the solution you'd like

As part of testing OTLP profile ingestion into Charmed Pyroscope, we developed a small `profilegen` script that generates synthetic profiling data.

We think there could be value in upstreaming this tool both as a testing utility and as a way to detect profiling signal changes early.

If this sounds useful, we would be happy to contribute the script upstream!

The issue proposes upstreaming a `profilegen` utility for synthetic profiling data and OTLP ingestion checks, but names no files or tests. Start by locating the repository's existing OTLP ingestion and profiling test utilities; done should include an upstream tool that generates usable synthetic profiles and verifies they are ingested correctly.

Written by the indexing model from the issue text.