text: Title: Web-gui: CNAME content does not allow leading asterisk or underscore
  Body: When trying to create CNAME records the web-gui denies using asterisk or underscore as a leading character in the content.
  
  Failing examples:
  ```
  _DMARC  3600  IN  CNAME  _DMARC.example.org.
  *.udp   3600  IN  CNAME  *.tcp.example.org.
  ```