Document performance degradation running under debugpy when not attached #1860

Given a use case such as this:

exec /.venv/bin/python3 -m debugpy --listen 0.0.0.0:5678 ${DEBUG_CMD} -m uvicorn --reload --host "$HOST" --port "$PORT" --log-level "$LOG_LEVEL" "$MODULE_NAME"

it would be nice to know how much of a performance hit we're getting by starting our code under debugpy, but not attaching to it. I've come across a situation where we might be running our code under debugpy in production, and I want to know how much this is hurting us. This does not seem to be covered by the current documentation.