Inform about Core Flood intersection

Problem/Motivation

See the parent task and this sibling task: #3330717: Use Core Flood Service for hard blocking users? for details.

In a first step, we should simply show information on the settings page to inform the user about possible overlaps and the https://www.drupal.org/project/flood_control module

Steps to reproduce

Proposed resolution

Add a warning message to the login_security settings page like this:

Due to historic reasons, login_security's functionality currently partially overlaps with Drupal Core's Flood functionality. If Drupal Core's flood limits are lower than the login_security limits, login_security may not work as expected. See <a href="https://www.drupal.org/project/login_security/issues/3330627" target="_blank">this issue</a> for technical details and implementation status.

Remaining tasks

User interface changes

API changes

Data model changes