PATCH verb is used when creating a namespace using server-side apply,
while POST verb is used when creating a namespace using client-side
apply.
The difference in path between the two ways to create a namespace led to
an inconsistency when calling webhooks. When server-side apply is used,
the request sent to webhooks has the field "namespace" populated with
the name of namespace being created. On the other hand, when using
client-side apply the "namespace" field is omitted.
This commit aims to make the behaviour consistent and populates the
"namespace" field when creating a namespace using POST verb (i.e.
client-side apply).
Kubernetes-commit: 3cb510e33eecbdc37aad14f121396ccfbf5268cb
618f4b129a