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/Program.cs

@@ -88,6 +88,7 @@ try
     }
 
     //AddEF Core dbcontext
+    var useDbMigration = Environment.GetEnvironmentVariable("MIGRATION_TEST_MODE") == true.ToString() || config.GetValue<bool>("UseDbMigration");
     var connStr = config.GetConnectionString(Key.Default) ?? throw new InvalidOperationException("There is no default connection string in appsettings.json.");
 
     builder.Services.AddDistributedSqlServerCache(options =>