Add migration support and update launch settings

Introduce `useDbMigration` variable in `Program.cs` to conditionally manage database migrations based on environment settings. Update `launchSettings.json` to include a new `httpsDbMigration` profile for testing with Swagger UI. Modify `appsettings.json` to add `UseDbMigration` setting and replace the "Dev" connection string with "DbMigrationTest" for migration testing.

EnvelopeGenerator.Web/Properties/launchSettings.json

@@ -16,7 +16,7 @@
         "ASPNETCORE_ENVIRONMENT": "Development"
       }
     },
-    "swagger": {
+    "https": {
       "commandName": "Project",
       "launchBrowser": true,
       "launchUrl": "swagger",
@@ -25,6 +25,17 @@
       },
       "dotnetRunMessages": true,
       "applicationUrl": "https://localhost:7202;http://localhost:5009"
+    },
+    "httpsDbMigration": {
+      "commandName": "Project",
+      "launchBrowser": true,
+      "launchUrl": "swagger",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development",
+        "MIGRATION_TEST_MODE": "true"
+      },
+      "dotnetRunMessages": true,
+      "applicationUrl": "https://localhost:7202;http://localhost:5009"
     }
   },
   "iisSettings": {