Error calling sync triggers (BadRequest) during func azure functionapp publish

Deploy fails for a function app and I cannot figure out what is wrong. The portal says

"Azure Functions runtime is unreachable"

The reason is because of an `ArgumentException` being thrown in Startup.cs due to missing configuration values. I found this out by trial and error.

So I would like to know if errors during startup is logged somewhere or if they are just ignored?

```
PS C:\Users\marti\RiderProjects\ContactService\ContactService> func azure functionapp publish bsl-contactservice-dev
Microsoft (R) Build Engine version 16.8.0+126527ff1 for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

Determining projects to restore...
All projects are up-to-date for restore.
ContactService -> C:\Users\marti\RiderProjects\ContactService\ContactService\bin\publish\ContactService.dll

Build succeeded.
0 Warning(s)
0 Error(s)

Time Elapsed 00:00:01.73

Getting site publishing info...
Creating archive for current directory...
Uploading 16,07 MB [##############################################################################]
Upload completed successfully.
Deployment completed successfully.
Syncing triggers...
Syncing triggers...
Syncing triggers...
Syncing triggers...
Syncing triggers...
Syncing triggers...
Error calling sync triggers (BadRequest). Request ID = '8d8f5875-e5ed-42f2-bac0-ac2392210e7c'.
```

Reproduce the deployment with `func azure functionapp publish` and the shown sync-triggers failure, then inspect the function app's `Startup.cs` where the `ArgumentException` occurs. Determine whether startup errors are logged or suppressed during publishing, and define done as making that failure diagnosable to the person running the command.

Written by the indexing model from the issue text.