### Description

Replace the existing selects with multi-selects that allow you to filter multiple DAG run states and types at the same time, somewhat similar to my prototype:

![image](https://github.com/apache/airflow/assets/1842905/c4ec0793-1ccb-417d-989c-781997416f97)


### Use case/motivation

I'm not sure if it is just me, but sometimes I wish I was able to show multiple DAG run states, especially `running` and `failed`, at the same time. 
This would be especially helpful for busy DAGs on which I want to clear a few failed runs. Without the multi-select, if I switch from `failed` to `running` DAG runs, I need to orient myself again to find the run I just cleared (assuming there are lots of other running DAG runs). _With_ the multi-select, the DAG run I just cleared stays in the same spot and I can check the logs, while clearing some other failed runs.

I'm not sure we need a multi-select for DAG run types as well. I'd tend to say no, but maybe someone else has a use-case for that.

### Related issues

_No response_

### 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)

"""Import variables."""
        try:
            variable_dict = json.loads(request.files["file"].read())
            action_on_existing = request.form.get("action_if_exists", "overwrite").lower()
        except Exception:
            self.update_redirect()
            flash("Missing file or syntax error.", "error")
            return redirect(self.get_redirect())
        else:
            existing_keys = set()
            if action_on_existing != "overwrite":
                existing_keys = set(
                    session.scalars(select(models.Variable.key).where(models.Variable.key.in_(variable_dict)))
                )
            if action_on_existing == "fail" and existing_keys:
                failed_repr = ", ".join(repr(k) for k in sorted(existing_keys))
                flash(f"Failed. The variables with these keys: {failed_repr}  already exists.")