Solve executor state mismatch / task killed externally

### Body Users have long been confused by log messages along the lines of "task state changed externally", or something about executor state mismatch, where the thing that emits the log is essentially saying, 🤷 , no clue what happened sorry. E.g. see here https://airflow.apache.org/docs/apache-airflow/stable/troubleshooting.html#task-state-changed-externally This should mostly be avoidable. If a task was killed by external user action, why do we not have a signal of that recorded somewhere (e.g. on the TI object or in event log), and why can't the executor (or task process or whatever) _see_ that and then either not have to log such a message, or log a more helpful one that says exactly what happened. ### Committer - [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.