Add corev1 resources specific steps

[garomonegro]

We need to add more specific step syntax and implementation around core/v1 resources like pods, nodes, etc.

The following generic resource syntax are good examples:

<GK> I <operation> the resource <filename>.yaml
<GK> the resource <filename> should be <state>
<GK> the resource <filename> [should] converge to selector <complete key>=<value>
<GK> the resource <filename> condition <condition type> should be (true|false)
<GK> I update a resource <filename> with <complete key> set to <value>

More details about those here.