### 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
flash,
    g,
    jsonify,
    make_response,
    redirect,
    render_template,
    request,
    send_from_directory,
    session as flask_session,
    url_for,
)
from flask_appbuilder import BaseView, ModelView, expose
from flask_appbuilder.actions import action
from flask_appbuilder.fieldwidgets import Select2Widget
from flask_appbuilder.models.sqla.filters import BaseFilter
from flask_appbuilder.security.decorators import has_access
from flask_appbuilder.security.views import (
    PermissionModelView,
    PermissionViewModelView,
    ResetMyPasswordView,
    ResetPasswordView,
    RoleModelView,
    UserDBModelView,
    UserInfoEditView,
    UserLDAPModelView,
    UserOAuthModelView,
    UserOIDModelView,
    UserRemoteUserModelView,
    UserStatsChartView,
    ViewMenuModelView,