Checkmk Werk 15190: Allow agent registration using an IP address as hostname

ID: 15190 Title: Allow agent registration using an IP address as hostname Component: Checks & agents Level: 1 Class: Bug fix Version: 2.1.0p27 IP addresses can now be used as hostnames again when registering new agents with the Agent Controller. This fixes a regression that was introduced with Checkmk 2.1.0p12 / Werk #14385.