### Description

https://github.com/apache/airflow/pull/17946 implements a `/robots.txt` endpoint to block search engines crawling Airflow - in the cases where it is (accidentally) exposed to the public Internet.

If we record any GET requests to that end-point we'd have a strong warning flag that the deployment is exposed, and could issue a warning in the UI, or even enable some kill-switch on the deployment. 

Some deployments are likely intentionally available and rely on auth mechanisms on the `login` endpoint, so there should be a config option to suppress the warnings.

An alternative approach would be to monitor for requests from specific user-agents used by crawlers for the same reasons

### Use case/motivation

People who accidentally expose airflow have a slightly higher chance of realising they've done so and tighten their security.

### 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)

airflow/www/views.py
"""Duration calculation."""
        end_date = self.get('end_date')
        start_date = self.get('start_date')
        difference = '0s'
        if start_date and end_date:
            difference = td_format(end_date - start_date)
        return difference
    formatters_columns = {
        'execution_date': wwwutils.datetime_f('execution_date'),
        'state': wwwutils.state_f,
        'start_date': wwwutils.datetime_f('start_date'),
        'end_date': wwwutils.datetime_f('end_date'),
        'queued_at': wwwutils.datetime_f('queued_at'),
        'dag_id': wwwutils.dag_link,
        'run_id': wwwutils.dag_run_link,
        'conf': wwwutils.json_f('conf'),
        'duration': duration_f,
    }
    @action('muldelete', "Delete", "Are you sure you want to delete selected records?", single=False)
    @action_has_dag_edit_access
    def action_muldelete(self, items: List[DagRun]):