WARNING about not pinned plugins - only in default life cycle

Context

Based on MNG-6562 Maven will produce a WARNING if plugin(s) are not defined with version in pluginManagement.

Problem

If Maven is called like this:

mvn clean

there is no such WARNING emitted (for example for the maven-clean-plugin).

Goal

We should emit a warning(s) for each life cycle clean and also for site life cycle in such cases.