### 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
"""View to show records from Variable table"""
    route_base = '/variable'
    list_template = 'airflow/variable_list.html'
    edit_template = 'airflow/variable_edit.html'
    datamodel = AirflowModelView.CustomSQLAInterface(models.Variable)  
    class_permission_name = permissions.RESOURCE_VARIABLE
    method_permission_name = {
        'add': 'create',
        'list': 'read',
        'edit': 'edit',
        'delete': 'delete',
        'action_muldelete': 'delete',
        'action_varexport': 'read',
    }
    base_permissions = [
        permissions.ACTION_CAN_CREATE,
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_EDIT,
        permissions.ACTION_CAN_DELETE,
        permissions.ACTION_CAN_ACCESS_MENU,
    ]
    list_columns = ['key', 'val', 'description', 'is_encrypted']
    add_columns = ['key', 'val', 'description']
    edit_columns = ['key', 'val', 'description']
    search_columns = ['key', 'val']
    base_order = ('key', 'asc')
    def hidden_field_formatter(self):