Add syslog-ng state and execution module

Syslog-ng is an open source logging daemon. This pull request contains a state and an execution modul for it.

The state module is able to generate syslog-ng configuration from YAML format, and start, stop or reload syslog-ng. The commit id of the patch is: 80f84196231db7f1a232194e3dcb6eacb3ae3583.

The execution module can check the version of the generated configuration or get some information about syslog-ng, e.g. version.

This pull request requires https://github.com/saltstack/salt/pull/14032 to be accepted.
I tried to find the most natural representation of a syslog-ng configuration as a YAML document. I use this kind of format, because syslog-ng's configuration can be deeply nested.