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

### Which sample?

[Instrumenting Cloud Functions for Firebase with Open Telemetry](https://github.com/firebase/functions-samples/tree/4c058eac88a9e95f4e2148e0e5a22ffe15426c9b/2nd-gen/instrument-with-opentelemetry#instrumenting-cloud-functions-for-firebase-with-open-telemetry)

### What is the issue with this sample's docs?

@taeold had a great [talk](https://www.youtube.com/watch?v=61WC7urgvQ4) 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](https://github.com/open-telemetry/opentelemetry-js/issues/1739) 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?