Restore support of starting mapped tasks from triggerer

### Body #48006 disabled starting mapped tasks from triggerer because it was crashing the scheduler (https://github.com/apache/airflow/issues/47735). It was discovered late in the airlfow 3 beta process so, disabling it was a reasonable choice. When time permits, one could look into restoring this capability, perhaps with limitations. ### Committer - [x] I acknowledge that I am a maintainer/committer of the Apache Airflow project.