### Overview
Some Executors, currently a subset of the local Executors, run in a single threaded fashion and have certain limitations and requirements, many of which are hardcoded. To add a new single threaded Executor would require changes to core Airflow code.
Note: This coupling often shows up with SQLite compatibility checks since it does not support multiple connections.
### Examples
- **2a**) SQLite check done in configuration.py: https://github.com/apache/airflow/blob/26f94c5370587f73ebd935cecf208c6a36bdf9b6/airflow/configuration.py#L412-L419
- **2b**) When running in standalone mode SQLite compatibility is checked: https://github.com/apache/airflow/blob/26f94c5370587f73ebd935cecf208c6a36bdf9b6/airflow/cli/commands/standalone_command.py#L160-L165
- **2c**) Sensors in `poke` mode can block execution of DAGs when running with single process Executors, currently hardcoded to DebugExecutor (although should also include SequentialExecutor): https://github.com/apache/airflow/blob/27e2101f6ee5567b2843cbccf1dca0b0e7c96186/airflow/sensors/base.py#L243
### Proposal
A static method or attribute on the Executor class which can be checked by core code.

There is a precedent already set with the `supports_ad_hoc_ti_run` attribute, see:
https://github.com/apache/airflow/blob/fb741fd87254e235f99d7d67e558dafad601f253/airflow/executors/kubernetes_executor.py#L435 https://github.com/apache/airflow/blob/26f94c5370587f73ebd935cecf208c6a36bdf9b6/airflow/www/views.py#L1735-L1737
sensor.clear()
        
        date3 = date1 + timedelta(seconds=sensor.poke_interval) * 2 + sensor.retry_delay
        time_machine.coordinates.shift(sensor.poke_interval + sensor.retry_delay.total_seconds())
        self._run(sensor)
        tis = dr.get_task_instances()
        assert len(tis) == 2
        for ti in tis:
            if ti.task_id == SENSOR_OP:
                assert ti.state == State.UP_FOR_RESCHEDULE
                
                task_reschedules = TaskReschedule.find_for_task_instance(ti)
                assert len(task_reschedules) == 1
                assert task_reschedules[0].start_date == date3
                assert task_reschedules[0].reschedule_date == date3 + timedelta(seconds=sensor.poke_interval)
                assert task_reschedules[0].try_number == 2
            if ti.task_id == DUMMY_OP:
                assert ti.state == State.NONE
        
        time_machine.coordinates.shift(sensor.poke_interval)
        self._run(sensor)
        tis = dr.get_task_instances()
        assert len(tis) == 2
        for ti in tis:
            if ti.task_id == SENSOR_OP:
                assert ti.state == State.SUCCESS
            if ti.task_id == DUMMY_OP:
                assert ti.state == State.NONE
    @pytest.mark.parametrize("mode", ["poke", "reschedule"])
    def test_should_include_ready_to_reschedule_dep(self, mode):