syslog-ng: add abstractions/python for python-parser
When running syslog-ng with a defined python-parser, it needs access to python libraries.
For details about python-parser, see https://www.syslog-ng.com/community/b/blog/posts/format-your-log-messages-in-python
References: https://github.com/balabit/syslog-ng/issues/2625
I propose this patch for 2.10..master