chore(queue): use schema config instead of search_path and application_name to configure the database schema (#10075)

Removes manual schema and application name setup via raw SQL and
switches to using River’s built-in schema configuration.

# Which Problems Are Solved

River provides a configuration flag to set the schema of the queue.
Zitadel sets the schema through database statements which is not needed
anymore.

# How the Problems Are Solved

Set the schema in the river configuration and removed old code

internal/queue/migrate.go

@@ -27,11 +27,10 @@ func (m *Migrator) Execute(ctx context.Context) error {
 		return err
 	}
 
-	migrator, err := rivermigrate.New(m.driver, nil)
+	migrator, err := rivermigrate.New(m.driver, &rivermigrate.Config{Schema: schema})
 	if err != nil {
 		return err
 	}
-	ctx = WithQueue(ctx)
 	_, err = migrator.Migrate(ctx, rivermigrate.DirectionUp, nil)
 	return err