FIX: Add wrapTraceContext to onChangedOperation to enable traceId on onDocumentUpdated

[JonatanSalas]

Description

When using firebase-functions v2 traceId is missing for Firestore triggers like onDocumentUpdated.

After a deep dive into the repository's code I've found that there's a difference.

onDocumentCreated relies in the method onOperation which wraps the event handler with the function wrapTraceContext that injects the trace information.

On the other side, onDocumentUpdated relies in the method onChangedOperation which executes the event handler without using the wrapTraceContext function. I don't know if this is intentional, but this is a problem of those who are heavy users of firebase functions under the v2 because in previous version the traceId was available.

I've adapted the code to make onChangedOperation use the wrapTraceContext function. With that line I think we can solve the issue of missing traceId in onDocumentUpdated.

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