Log the exception's message to Application Insights

I'm using C# Azure Functions.
All exceptions are/shall be logged to our Application Insights. We monitor those logs in the AI by another tool.

I've created a very simple function:
```
[FunctionName(nameof(Text_ExceptionLogging))]
public FunctionResult Text_ExceptionLogging([HttpTrigger(AuthorizationLevel.Function, "get")] HttpRequestMessage request, ExecutionContext context)
{
var a = SettingsManager.GetValue("-invalid-");
return true;
}
```
`SettingsManager.GetValue` will throw an exception saying this value is not configured through the Azure Portal. When running the function and I'm connected to the output (eg. viewing the local console or the Log stream portal), I can see that message:

> 2021-11-26T00:00:00.110 [Error] Executed 'Text_ExceptionLogging' (Failed, Id=00000000-0000-0000-0000-000000000000, Duration=1ms)Configuration key -invalid- not found [...]

But it's not fully logged to the Application Insights:

column | value
-- | --
timestamp [UTC] | 2021-11-26T00:00:00.311Z
message | Executed 'Text_ExceptionLogging' (Failed, Id=00000000-0000-0000-0000-000000000000, Duration=1ms)
severityLevel | 3
cloud_RoleName | MyApp
operation_Name | Text_ExceptionLogging

If the exception message is not logged, I can't see / filter for it. I've already created a wrapper method some time ago, that catches all exceptions, logs its message and stack trace in separated actions using the built-in logger (which writes to the Application Insights), so I'm able to see additional information. The problem is that this wrapper method was not used here. Sure, I can add this to my `Text_ExceptionLogging` function too, but I think that logging the exception's message would be useful in general for everyone. I can see it in the console, in the log stream, so why wouldn't it be available in AI too?

Reproduce the C# Azure Function with SettingsManager.GetValue("-invalid-") and compare the local console or Log stream output with the Application Insights record. Done means the exception message, including the missing configuration key, is present in Application Insights and can be filtered there.

Written by the indexing model from the issue text.