Fixed function parameter not being used for LoadFromFile (#1803)

### Motivation and Context
While trying to reuse the Settings class used in the C# notebooks to
load the Kernel configuration, I saw the parameter to specify a file was
not properly used.


### Description
Very simple changes as I just updated the code to use the function
parameter instead of the Class variable Default
It is in the notebook part so no build nor tests. Notebooks are still
working.

### Contribution Checklist
<!-- Before submitting this PR, please make sure: -->
- [x] The code builds clean without any errors or warnings
- [x] The PR follows SK Contribution Guidelines
(https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
- [x] The code follows the .NET coding conventions
(https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions)
verified with `dotnet format`
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

Co-authored-by: Shawn Callegari <36091529+shawncal@users.noreply.github.com>

samples/notebooks/dotnet/config/Settings.cs

@@ -131,16 +131,16 @@ public static async Task<string> AskOrg(bool _useAzureOpenAI = true, string conf
     public static (bool useAzureOpenAI, string model, string azureEndpoint, string apiKey, string orgId)
         LoadFromFile(string configFile = DefaultConfigFile)
     {
-        if (!File.Exists(DefaultConfigFile))
+        if (!File.Exists(configFile))
         {
-            Console.WriteLine("Configuration not found: " + DefaultConfigFile);
+            Console.WriteLine("Configuration not found: " + configFile);
             Console.WriteLine("\nPlease run the Setup Notebook (0-AI-settings.ipynb) to configure your AI backend first.\n");
             throw new Exception("Configuration not found, please setup the notebooks first using notebook 0-AI-settings.pynb");
         }
 
         try
         {
-            var config = JsonSerializer.Deserialize<Dictionary<string, string>>(File.ReadAllText(DefaultConfigFile));
+            var config = JsonSerializer.Deserialize<Dictionary<string, string>>(File.ReadAllText(configFile));
             bool useAzureOpenAI = config[TypeKey] == "azure";
             string model = config[ModelKey];
             string azureEndpoint = config[EndpointKey];