The original ClusterProperty documentation was hard to follow and left some key
questions unanswered, such as where the custom resource should be placed, how it
actually ties to a cluster, and what is explicitly defined versus left
unspecified.

For me, this meant that even though I understood ClusterProperty could identify
a cluster, I struggled to grasp its lifecycle and practical usage without
digging into the KEP directly.

This PR expands the documentation with lifecycle rules, constraints, use cases,
and operational guidance, so readers can build an intuitive understanding of
ClusterProperty without having to cross-reference the KEP.

I hope this helps others who may run into the same confusion and need a more
practical, approachable explanation.

Unlike the exhaustive and formal style of the KEP, this documentation focuses
on clarity and practical understanding, so that readers can quickly grasp what
ClusterProperty is and how to use it.