Error with tld in CAA DNS-Entry Name

Summary

The feature to create caa with coma separation has a bug: https://git.ispconfig.org/ispconfig/ispconfig3/-/blob/develop/interface/lib/plugins/system_config_dns_ca_plugin.inc.php?ref_type=heads

Steps to reproduce

1. Create a CAA-Entry with name "test.example.com." for Domain "example.com"
2. ISPConfig would automatically create a second DNS-Entry too with name ".example.com.example.com.". The Zone file is broken.

Correct behaviour

Proposed fix

I will provide a merge request