"Queue up new tasks" equivalent in CLI / REST API

### Description

Suggestion to add a new command in the CLI / REST API to reproduce the "Queue up new tasks" action that can be trigger within the web UI, with `start_date` and `end_date` parameters to allow running this action accross all dag runs lying a given period.

For the CLI, it could be `airflow dags queue_up_new_tasks` or `airflow dags reload` for instance.

### Use case/motivation

Right now, when we add new tasks to an existing dag containing existing dag runs, it is not straightforward to run these newly added tasks in the existing/previous dag runs.

Two workarounds :
- `airflow dags backfill` but not satisfying as it transforms "scheduled" existing dags run into "backfill" dag runs, which prevent us from interacting with them through the web UI (like clearing tasks, etc.)
- `airflow tasks render` followed by `airflow tasks clear` but it is not convenient as the `render` command is only working for one specific execution_date (or run_id) at a time.

Or maybe there are already solutions par that ?

### Related issues

https://github.com/apache/airflow/discussions/30435#discussioncomment-8856597

### 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)

Start by comparing the web UI “Queue up new tasks” action with the existing `airflow dags backfill` and `airflow tasks render`/`clear` commands. Trace the CLI and REST API entry points involved, then clarify the date-range and existing-DAG-run behavior; done means the action is available through the requested interfaces without converting scheduled runs to backfills.

Written by the indexing model from the issue text.