Add Zabbix Proxy recipe

[odyssey4me]

It'd be highly useful to also have a recipe to deploy a Zabbix proxy. The recipe should support being in an environment which either includes a server or does not.

In the case where the environment includes a Zabbix server, the proxy should automatically find its server.
In the case where the environment does not include a Zabbix server, the server's details should be provided through attributes.

Client Agents should be able to find either the server or the proxy. The preference should be set through an agent recipe attribute.