Add CustomResource to Python SDK

[lblackstone]

Fixes #326

Based on #327

This adds CR support to the Python SDK. Here's what it currently looks like:

from pulumi_kubernetes.apiextensions import CustomResource
from pulumi_kubernetes.apiextensions.v1beta1 import CustomResourceDefinition

crd = CustomResourceDefinition(
    "foobar",
    metadata={
        "name": "foobars.stable.example.com"
    },
    spec={
        "group": "stable.example.com",
        "version": "v1",
        "scope": "Namespaced",
        "names": {
            "plural": "foobars",
            "singular": "foobar",
            "kind": "FooBar",
            "shortNames": ["fb"]
        }
    }
)

cr = CustomResource(
    "my-new-foobar-object",
    api_version="stable.example.com/v1",
    kind="FooBar",
    metadata={
        "namespace": namespace
    },
    spec={ "foo": "such amaze", "bar": "wow" }
)

Compare to the NodeJS SDK:

import * as k8s from "@pulumi/kubernetes";

new k8s.apiextensions.v1beta1.CustomResourceDefinition("foobar", {
    metadata: { name: "foobars.stable.example.com" },
    spec: {
        group: "stable.example.com",
        version: "v1",
        scope: "Namespaced",
        names: {
            plural: "foobars",
            singular: "foobar",
            kind: "FooBar",
            shortNames: ["fb"]
        }
    }
});

new k8s.apiextensions.CustomResource(
    "my-new-foobar-object",
    {
        apiVersion: "stable.example.com/v1",
        kind: "FooBar",
        metadata: {
          namespace: namespace.metadata.name,
        },
        spec: { foo: "such amaze", bar: "wow" }
    },
);

[lblackstone]

@hausdorff @metral Ok, I think this is ready to go. Semantics are equivalent to the NodeJS SDK, and I tested both with manual creation of CRD/CR and from a YAML manifest.

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: foos.bar.example.com
spec:
  group: bar.example.com
  versions:
    - name: v1
      served: true
      storage: true
  scope: Namespaced
  names:
    plural: foos
    singular: foo
    kind: Foo
---
apiVersion: bar.example.com/v1
kind: Foo
metadata:
  name: foobar
spec:
  foo: "such amaze"
  bar: "wow"

results in the following:

     Type                                                            Name                   Status
 +   pulumi:pulumi:Stack                                             yaml-test-python-yaml  created
 +   ├─ kubernetes:yaml:ConfigFile                                   yaml-test              created
 +   │  ├─ kubernetes:apiextensions.k8s.io:CustomResourceDefinition  foos.bar.example.com   created
 +   │  └─ kubernetes:bar.example.com:Foo                            foobar                 created
 +   └─ kubernetes:core:Namespace                                    ns                     created

Resources:
    + 5 created

[swgillespie]

I suspect that this is going to burn us in the future, though I'm not sure what we can do about it now.

We use the _CASING tables to convert to and from kubernetesCase to python_case, but these tables are derived from the OpenAPI spec. If a custom resource defines a property that isn't in the upstream Kubernetes openAPI spec, it's going to stay in kubernetesCase, which is going to be annoying.

I don't think there's anything to do here but it's worth noting this possibility.