[In Portal] EventGrid Trigger execution failed with NotImplementedException

### Repro steps

1. Create new Function App with PowerShell Core stack
2. Add new function in portal
3. Select `EventGrid Trigger` function template
4. Confirm `Microsoft.Azure.WebJobs.Extensions.EventGrid` installing dialog
5. Select created function and click `Run` button

### Error log

```
2020-01-07T16:59:11 Welcome, you are now connected to log-streaming service. The default timeout is 2 hours. Change the timeout with the App Setting SCM_LOGSTREAM_TIMEOUT (in seconds).
2020-01-07T16:59:20.395 [Information] Executing 'Functions.EventGridTrigger1' (Reason='This function was programmatically called via the host APIs.', Id=5fb87d7b-9fa5-4ab2-a2ec-cb7f24c6621e)
2020-01-07T16:59:20.515 [Error] Executed 'Functions.EventGridTrigger1' (Failed, Id=5fb87d7b-9fa5-4ab2-a2ec-cb7f24c6621e)
The method or operation is not implemented.
```

### Addtional information

- Runtime version: 2.0.12888.0 (~2)
- Platform: Windows
- ASP Tier: Consumption
- Region: West US 2

### Workaround

Downgrade `Microsoft.Azure.WebJobs.Extensions.EventGrid` version `2.1.0` to `2.0.0`