Refactor email account configuration for multi-account support

Refactored `EmailAccountDto` to represent a single account with
immutable properties and added an `Id` field. Introduced
`EmailAccountsOptions` to manage multiple accounts and bound it
to the `EmailAccounts` configuration section.

Updated `DependencyInjection` to register `EmailAccountsOptions`
and removed the old single-account binding. Refactored
`LimilabsEmailService` to use `EmailAccountsOptions` and select
the appropriate account dynamically.

Replaced the `EmailAccount` section in `appsettings.Secrets.json`
with a new `EmailAccounts` section supporting multiple accounts.
Added a package reference for `Microsoft.Extensions.Options.
ConfigurationExtensions` to support the options pattern.

src/presentation/DigitalData.MessagingService.API/Program.cs

@@ -67,10 +67,6 @@ try
     // Register Infrastructure layer (RabbitMQ, Repositories, etc.)
     builder.Services.AddInfrastructure(builder.Configuration);
 
-    // Register EmailAccount configuration (IOptions<EmailAccountDto>)
-    builder.Services.Configure<EmailAccountDto>(
-        builder.Configuration.GetSection("EmailAccount"));
-
     builder.Services.AddControllers();
 
     builder.Services.AddEndpointsApiExplorer();

src/presentation/DigitalData.MessagingService.API/appsettings.Secrets.json

@@ -15,13 +15,18 @@
     "DlqExchangeName": "emailprofiler.emails.dlq",
     "DlqRoutingKey": "email.outbox.dlq"
   },
-  "EmailAccount": {
-    "Username": "test-flow@digitaldata.works",
-    "Password": "ddemail108",
-    "PasswordEncrypted": false,
-    "SmtpServer": "kundencenter.triplew.de",
-    "SmtpPort": 465,
-    "SmtpUseSsl": true,
-    "UseOAuth2": false
+  "EmailAccounts": {
+    "Accounts": [
+      {
+        "Name": "1",
+        "Username": "test-flow@digitaldata.works",
+        "Password": "ddemail108",
+        "PasswordEncrypted": false,
+        "SmtpServer": "kundencenter.triplew.de",
+        "SmtpPort": 465,
+        "SmtpUseSsl": true,
+        "UseOAuth2": false
+      }
+    ]
   }
 }