Define a scope for ZMON agent

[mohabusama]

ZMON agent is currently used to discover Kubernetes resources and Postgresql resources running on Kubernetes. Eventually zmon-aws-agent should be part of this unified agent as well.

The problem about mixing infrastructure discovery with applications/DB discovery is that it leads to:

• Slower development and release cycles.
• Bugs and issues that is not fully related to ZMON.

The idea is to define the following:

• ZMON discovery scope is mainly related to infrastructure discovery.
• ZMON agent discovery could be extended (one way or another) by external users.
• ZMON agent should make infrastructure resources available to all extensible solutions.