Extensibility: don't hardcode namespace and name in relations/dataSources

[Wawrzyn321]

Description

User cannot use the current resource to select a name and namespace in relation.

(The namespace defaults to current resource's namespace, if set explicitly to null it targets resources in all namespaces (and works as expected for clusterwide ones)).

Workaround

Query all the namespaces / resources in a namespace and filter them with selector/filter field - here we can do Jsonata magic, but it's more complex and generates higher traffic.

Reasons

While it serves it's purpose, we want to cover more usecases.