### 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)

tests/www/views/test_views_base.py
last_heartbeat = timezone.utcnow() - datetime.timedelta(minutes=1)
    job = BaseJob(
        job_type='SchedulerJob',
        state='running',
        latest_heartbeat=last_heartbeat,
    )
    with create_session() as session:
        session.query(BaseJob).filter(
            BaseJob.job_type == 'SchedulerJob',
        ).update({'latest_heartbeat': last_heartbeat - datetime.timedelta(seconds=1)})
        session.add(job)
    yield 'unhealthy', last_heartbeat.isoformat()
    with create_session() as session:
        session.query(BaseJob).filter(
            BaseJob.job_type == 'SchedulerJob',
            BaseJob.state == 'running',
            BaseJob.latest_heartbeat == last_heartbeat,
        ).delete()
@pytest.fixture()
def heartbeat_not_running():