Using a settings file with a different name is not working.

Function App name: microServiceBus.functions
Tools used: VS2022 - Version 17.4.4 & Version 17.7.4
.Net runtime: 6
Runtime: dotnet-isolated
Language: C#
Core Tools Version: 4.0.5390 Commit hash: N/A (64-bit)
Function Runtime Version: 4.25.3.21264

We have an function app used by many customers, hence we've had to updated the `local.settings.json` dependin on which the customer we've been working with. Upon migrating from v4 In-proc to v4 isolated we've instead created multiple settings files, one for each customer as this has worked fine for our web applications. However, using a settings file with a different name is not working.

```csharp
var host = new HostBuilder()
.ConfigureAppConfiguration((context, config) => {
//config.AddJsonFile("local.settings.json", optional: true);
config.AddJsonFile("local.settings.CUSTOMER.json", optional: true);

config.AddEnvironmentVariables();
})
ConfigureLogging(logging => ...)
.ConfigureFunctionsWorkerDefaults()
.ConfigureServices((context, services) => ...)
.Build();

host.Run();
```
Behavior:
If the `local.settings.json` does not exist, the process will not start with the following error:
```bash
Azure Functions Core Tools
Core Tools Version: 4.0.5390 Commit hash: N/A (64-bit)
Function Runtime Version: 4.25.3.21264

Can't determine project language from files. Please use one of [--csharp, --javascript, --typescript, --java, --python, --powershell, --custom]
Can't determine project language from files. Please use one of [--csharp, --javascript, --typescript, --java, --python, --powershell, --custom]
Can't determine project language from files. Please use one of [--csharp, --javascript, --typescript, --java, --python, --powershell, --custom]
[2023-10-06T10:30:41.620Z] Microsoft.Azure.WebJobs.Host: Error indexing method 'Functions.IncidentHandler_SendEmail'. Microsoft.Azure.WebJobs.Host:
```
Interestingly, it seams the configuration is evaluated before the `ConfigureAppConfiguration` method is executed, as if I set a breakpoint in the method I can se the output of funciton list before the breakpoint is hit.