We are getting many transient error warnings in production

```
Transient error <StatusCode.UNAVAILABLE: (14, 'unavailable')> encountered while exporting metrics, retrying in 1s.
```

but unfortunately they don't have enough information to debug the issue, as we have two exporters, one exporting to our internal metric system and another one exporting to Uptrace.

In this PR we add the endpoint to the warning. That would allow us to better debug tghe issue and rule out faulty parts ion our systems.

requested a review from a team

sk- changed the title feat: incluse endpoint in grpc transient error warning feat: include endpoint in grpc transient error warning