Create initial overlay structure
Add net-analyzer/zabbix (1.8.20)

This is a heavily revised ebuild, based on our internally used which was
in turn based on the last 1.8.16 ebuild in gentoo-x86.

Notable changes:

* use EAPI 5 with REQUIRED_USE, SLOT dependencies, etc.
* drop Oracle support completely
* drop static building support, if required, make sure to use
  static-libs for the dependencies
* add patch from Fedora to support fping3