Refactor email account handling for dynamic resolution

Reintroduced `EmailAccountDto` with conditional compilation to support both .NET and non-.NET environments. Updated `IEmailService` to accept `EmailAccountDto` as the sender, replacing reliance on pre-configured SMTP credentials.

Added `GetSenderQuery` and its handler to dynamically resolve email accounts based on `Id` or `Username`. Introduced `GetSenderQueryValidator` for validation, ensuring proper usage of the query.

Modified `SendEmailCommand` to include sender resolution via MediatR. Updated `OutgoingEmailEvent` to include sender information and adjusted `OutgoingEmailConsumer` and `LimilabsEmailService` to use the dynamically resolved sender.

Updated `EmailMappingProfile` to ignore the `Sender` property during mapping. Replaced `Name` with `Id` in `appsettings.Secrets.json` for email accounts. Removed the old `EmailAccountDto` folder and performed general cleanup and restructuring.

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

@@ -18,7 +18,7 @@
   "EmailAccounts": {
     "Accounts": [
       {
-        "Name": "1",
+        "Id": "1",
         "Username": "test-flow@digitaldata.works",
         "Password": "ddemail108",
         "PasswordEncrypted": false,