refactor ServiceCollectionExtensions

StorageAccountExtensions don't need to exist in their own file.

Related to: aliencube#319

src/AzureOpenAIProxy.ApiApp/Extensions/ServiceCollectionExtensions.cs

@@ -165,6 +165,31 @@ public static IServiceCollection AddTableStorageService(this IServiceCollection
             return client;
         });
 
+        return services;
+    }
+
+        /// <summary>
+    /// Gets the storage account configuration settings by reading appsettings.json.
+    /// </summary>
+    /// <param name="services"><see cref="IServiceCollection"/> instance.</param>
+    /// <returns>Returns <see cref="StorageAccountSettings"/> instance.</returns>
+    public static IServiceCollection AddStorageAccountSettings(this IServiceCollection services)
+    {
+        services.AddSingleton<StorageAccountSettings>(sp => {
+            var configuration = sp.GetService<IConfiguration>()
+                ?? throw new InvalidOperationException($"{nameof(IConfiguration)} service is not registered.");
+
+            var settings = configuration.GetSection(AzureSettings.Name).GetSection(StorageAccountSettings.Name).Get<StorageAccountSettings>()
+                ?? throw new InvalidOperationException($"{nameof(StorageAccountSettings)} could not be retrieved from the configuration.");
+
+            if (string.IsNullOrWhiteSpace(settings.TableStorage.TableName) == true)
+            {
+                throw new InvalidOperationException($"{StorageAccountSettings.Name}.{TableStorageSettings.Name} is not defined.");
+            }
+
+            return settings;
+        });
+
         return services;
     }
 }