Add support for adhoc profiling mode

[abeaumont]

It'd be nice to make the integration work with adhoc profiling mode. In order to do so, the integration should be able to override the server address with the value in the PYROSCOPE_ADHOC_SERVER_ADDRESS environment variable, if it's defined.

Some reference info:

• documentation for adhoc support in HTTP API integrations
• adhoc profiling mode support in Java integration

[omarabid]

@abeaumont I'm a bit confused. What's the purpose of PYROSCOPE_ADHOC_SERVER_ADDRESS if the data is going to be saved locally?

[petethepig]

We're not going to implement it any time soon, so closing the issue.