Cannot set Json Serialization settings for Swagger UI/ OpenAPI schema when using IHostApplicationBuilder

**Describe the issue**
When using IHostApplicationBuilder, I cannot figure out how to adjust the Json Serialization setting to match what the function returns.

**To Reproduce**
Steps to reproduce the behavior:
1. Create a default HttpTrigger function app, which should use `FunctionsApplication.CreateBuilder(args)`
2. Change the Json Options to use a different naming policy
3. Update the HttpTrigger to return an object and add an appropriate `[OpenApiResponseWithBody]` attribute.
4. View the Swagger UI page, the respons object will not have appropriate formatting of names, while when you run the HtttpTrigger will return proper casing.

Program.cs
```csharp
var builder = FunctionsApplication.CreateBuilder(args);

builder.ConfigureFunctionsWebApplication();

builder.Services.AddMvc().AddJsonOptions(options =>
{
options.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower;
});

builder.Build().Run();
```

HttpTrigger1.cs
```csharp
namespace Company.Function
{
public class HttpTrigger1
{
private readonly ILogger _logger;

public HttpTrigger1(ILogger logger)
{
_logger = logger;
}

[Function("HttpTrigger1")]
[OpenApiOperation(operationId: "Run")]
[OpenApiResponseWithBody(HttpStatusCode.OK, "application/json", typeof(ResponseData), Description = "Some Data")]
public IActionResult Run([HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequest req)
{
_logger.LogInformation("C# HTTP trigger function processed a request.");
return new OkObjectResult(new ResponseData { AgeInYears = 18, FullName = "Fred" });
}
}

public class ResponseData
{
public int AgeInYears { get; set; }
public string FullName { get; set; } = string.Empty;
}
}
```

Current behavior:

You can see in the screen shot that the execution response used the proper casing (SnakeCaseLower), but the Example Value Response did not.

**Expected behavior**
It would be ideal for the same serializer to be used in both the response objects and the Swagger UI/OpenAPI schema.

Reproduce the mismatch using Program.cs and HttpTrigger1.cs with FunctionsApplication.CreateBuilder and SnakeCaseLower serialization. Compare the executed HttpTrigger response with the OpenAPI response example in Swagger UI; done means both use the same property naming, with an appropriate test or documented verification.

Written by the indexing model from the issue text.