[DOCS] for sample: Unclear if open telemetry is supported in cloud functions v1

[amkoehler]

Which sample?

Instrumenting Cloud Functions for Firebase with Open Telemetry

What is the issue with this sample's docs?

@taeold had a great talk at the firebase summit about cloud function observability. I started looking into adding open telemetry, but it's unclear to me if it will work properly in cloud functions v1. Daniel noted that a SIGTERM is sent with v2 and that allows for the telemetry SDK to be shut down properly. I found an open issue in the open-telemetry repo that makes me think it won't work as well in firebase functions v1.

Would it be possible to clarify this somewhere in the docs?