feat: add Migrator console project

- Dedicated HrynCo.NotificationService.Migrator console app
- Reads App:ConnectionString from config/env
- Calls db.Database.MigrateAsync() with clear log output
- Own Dockerfile (runtime:10.0 base, no SDK overhead)
- Replaces SDK volume-mount approach in docker-compose
- Added to solution with /docker/Migrator/ folder

Ref: IT-628

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

HrynCo.NotificationService.Migrator/appsettings.json

@@ -0,0 +1,18 @@
+{
+  "App": {
+    "ConnectionString": ""
+  },
+  "Serilog": {
+    "MinimumLevel": {
+      "Default": "Information",
+      "Override": {
+        "Microsoft": "Warning",
+        "Microsoft.EntityFrameworkCore": "Information"
+      }
+    },
+    "WriteTo": [
+      { "Name": "Console" }
+    ],
+    "Enrich": [ "FromLogContext" ]
+  }
+}