.get_endpoints.kind == "Endpoint" vs .get_endpoint(...).kind == "Endpoints"

[cben]

When getting a single entity, we return .kind as-is:

pry(main)> kclient.get_endpoint('docker-registry', 'default', as: :raw)[0..39]
=> "{\"kind\":\"Endpoints\",\"apiVersion\":\"v1\",\"m"
pry(main)> kclient.get_endpoint('docker-registry', 'default').kind
=> "Endpoints"
pry(main)> kclient.get_security_context_constraint('nonroot').kind
=> "SecurityContextConstraints"

For collections, k8s does not return individual .kind in each item, only a global list kind.
We do some magic to convert that to a singular .kind, without the List.
Somewhat confusingly, we do this on the EntityList pseudo-array, no .kind on individual item:

pry(main)> kclient.get_endpoints(as: :raw)[0..39]
=> "{\"kind\":\"EndpointsList\",\"apiVersion\":\"v1"
pry(main)> kclient.get_endpoints.kind
=> "Endpoint"
pry(main)> kclient.get_endpoints.first.kind
=> nil
pry(main)> kclient.get_security_context_constraints.kind
=> "SecurityContextConstraint"

The immediate bug here is "Endpoints" vs "Endpoint" and "SecurityContextConstraints" vs "SecurityContextConstraint" mismatch, because the single is already plural in k8s (see kubernetes/kubernetes#8115 (comment), kubernetes/kubernetes#18622, #81, #261 for background).
I'm not 100% sure which way to fix it, but I think the reason we "fixed" the double plural is merely we needed distinct get_foo / get_foos method names — which is a kubeclient concern that should not leak into .kind, it should always be a valid k8s API kind.

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The wider question I want to discuss (not necessarily here) is what's the purpose of this magic?

• The best use I envision is making it easy to feed the kind back to the API, which is not yet applicable much in kubeclient but is discussed on Allow different resources to use different apiVersion #208 etc.
  Towards that, I'd like us to provide the non-List .kind (and apiVersion?) inside every entity of the array, such that you don't have to care whether you obtained one from via List or Get operation. (And then potentially restore get_foos.kind to be "FooList".)

[cben]

Besides kind, neither the collection nor the individual items expose .api_version. It's simply lost.

[cben]

Split off the wider interface questions to #368.
This issue is only about the bugs get_endpoints.kind == "Endpoint" and get_security_context_constraints.kind == "SecurityContextConstraint".
Fixing in #366.