Make a version of TriggerDagRunOperator & ExternalTaskSensor that can target a separate Airflow instance

### Description

Do the same thing with external Airflow instances.

### Use case/motivation

I would like to use TriggerDagRunOperator & ExternalTaskSensor, or new objects, that behave the same but target a different Airflow instance.

### Related issues

This issue is partly covered in https://github.com/apache/airflow/issues/39463

I am considering solving it by using the Airflow API as mentioned in 39463

### Are you willing to submit a PR?

- [x] 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)

Start by reading the existing TriggerDagRunOperator and ExternalTaskSensor behavior, then review related issue 39463 and its Airflow API discussion. Define how equivalent objects would target a separate Airflow instance and verify that triggering and sensing work across instances; the issue does not name specific files or tests.

Written by the indexing model from the issue text.