### What do you see as an issue?

The documentation for zombie tasks https://airflow.apache.org/docs/apache-airflow/stable/core-concepts/tasks.html#zombie-undead-tasks is a bit abstract at the moment. There is a scope for enhancing the document by explaining how Airflow detects tasks as zombies

### Solving the problem

We can enhance the documentation by translating this query https://github.com/astronomer/airflow/blob/main/airflow/jobs/scheduler_job_runner.py#L1721 to a layman readable text in our documentation.

### Anything else

It might also help to add developer contribution steps to reproduce zombies locally.

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Stats.incr(
                    "scheduler.tasks.killed_externally",
                    tags={"dag_id": ti.dag_id, "task_id": ti.task_id},
                )
                msg = (
                    "Executor reports task instance %s finished (%s) although the "
                    "task says it's %s. (Info: %s) Was the task killed externally?"
                )
                self._task_context_logger.error(msg, ti, state, ti.state, info, ti=ti)
                
                try:
                    dag = self.dagbag.get_dag(ti.dag_id)
                    task = dag.get_task(ti.task_id)
                except Exception:
                    self.log.exception("Marking task instance %s as %s", ti, state)
                    ti.set_state(state)
                    continue
                ti.task = task
                if task.on_retry_callback or task.on_failure_callback:
                    request = TaskCallbackRequest(
                        full_filepath=ti.dag_model.fileloc,
                        simple_task_instance=SimpleTaskInstance.from_ti(ti),
                        msg=msg % (ti, state, ti.state, info),
                        processor_subdir=ti.dag_model.processor_subdir,
                    )
                    self.job.executor.send_callback(request)
                else:
                    ti.handle_failure(error=msg % (ti, state, ti.state, info), session=session)
        return len(event_buffer)
    def _execute(self) -> int | None: