Refactor backdoor handling and configuration loading

- Changed `TryGet` method return type from `bool?` to `bool` in `BackdoorExtensions.cs` for improved clarity.
- Updated configuration retrieval in `DependencyInjection.cs` to use `GetSection("backdoors")` for targeted loading.
- Added `backdoors.json` configuration file in `Program.cs` to enhance modularity and organization of settings.

src/DigitalData.Auth.API/Program.cs

@@ -27,6 +27,8 @@ try
 
     builder.Configuration.AddJsonFile("consumer-repository.json", true, true);
 
+    builder.Configuration.AddJsonFile("backdoors.json", true, true);
+
     var config = builder.Configuration;
 
     var apiParams = config.Get<AuthApiParams>() ?? throw new InvalidOperationException("AuthApiOptions is missing or invalid in appsettings.");