Add an option to run backfill while keeping dag execution suspended

### Description As a maintainer I would like to run backfill while suspending dag execution In order to backfill without executing dag every day In order to avoid useless computation and log ### Use case/motivation To perform a backfill, a dag must be triggered by cron and also it must be activated. In our case, we have a dag to reprocess old data, but we cannot run it dayly via cron because the data is not available. <img width="441" height="512" alt="Image" src="https://github.com/user-attachments/assets/03015bf9-e1f1-4789-a16e-b1ea02a67d1a" /> So we want to run only backfill while keeping daily dag execution suspended to avoid useless computation. Actually, we have an option `Unpause XXXX on trigger`. We could add a new option `Run backfill and keep dag suspended` to run only backfill ### Related issues _No response_ ### Are you willing to submit a 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)