opentelemetry-instrument command can cause recursive creation of subprocesses

[aabmass]

Describe your environment

Python3.9, linux.

Steps to reproduce
Using opentelemetry-instrument with any exporter or instrumentation which invokes a python subprocess during initialization. For example, the opentelemetry-exporter-gcp-trace exporter may invoke the gcloud (written in python) command in a subprocess to get project information and authentication tokens. The subprocess will then try to autoinstrument, creating a recursive loop of subprocesses being created.

What is the expected behavior?
Auto-instrumentation should not apply to subprocesses created in the initialize() phase of auto-instrumentation. The PYTHONPATH environment variable should have the sitecustomize.py dirname stripped out at the beginning of sitecustomize.py. This would prevent subprocesses from being autoinstrumented during setup, which can cause a loop.

What is the actual behavior?
PYTHONPATH is correctly stripped later on to avoid this

opentelemetry-python-contrib/opentelemetry-instrumentation/src/opentelemetry/instrumentation/auto_instrumentation/sitecustomize.py

Lines 120 to 125 in e9f83e1

	finally:
	environ["PYTHONPATH"] = sub(
	rf"{dirname(abspath(__file__))}{pathsep}?",
	"",
	environ["PYTHONPATH"],
	)

However, any subprocesses created in these lines will cause a loop.

Additional context
I can write a repro if necessary.