[Entities] Overlapping attribute names in different entity types

[dmitryax]

Specific example: In a multi-zonal cluster, k8s.cluster and k8s.node entities can both have cloud.availability_zone attribute with different values.

The problem described in more detail in https://docs.google.com/document/d/1sUwKJEwPB89uA1jUrX6ea-w-mIYNk5TJ8NuMOAZfW2M/edit?tab=t.0 by @quentinmit.

We discussed this problem as part of Additional requirements for entities data model during Entities SIG meeting on Jan 16 and agreed on a solution that is closer to what's described as potential solution A in https://docs.google.com/document/d/1sUwKJEwPB89uA1jUrX6ea-w-mIYNk5TJ8NuMOAZfW2M/edit?tab=t.0#heading=h.ezgpqjbuutx8.

cc @tigrannajaryan