fix: serialize smtp settings using runtime type not base class

JsonSerializer.Serialize(p.Settings) uses the compile-time type
EmailChannelSettings, producing only {EmailChannelType:1} in the DB.
Use p.Settings.GetType() to force runtime type so all SmtpChannelSettings
properties (Host, Port, Username, Password, etc.) are actually persisted.

Ref: IT-628

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.NotificationService.DAL.EF/Repositories/EmailChannelRepository.cs

@@ -89,7 +89,7 @@ internal sealed class EmailChannelRepository : EfRepository<EmailChannelEntity>,
             ServiceName = p.ServiceName,
             Priority = p.Priority,
             EmailChannelType = p.EmailChannelType,
-            SettingsJson = JsonSerializer.Serialize(p.Settings),
+            SettingsJson = JsonSerializer.Serialize(p.Settings, p.Settings.GetType()),
             DailyLimit = p.DailyLimit,
             MonthlyLimit = p.MonthlyLimit,
             WarnThresholdPercent = p.WarnThresholdPercent,