Kubernetes deployments on new clusters will now have
a separate namespace per project environment, instead
of sharing a single namespace for the project.
Behaviour of existing clusters is unchanged.
All new functionality is controlled by the
:kubernetes_namespace_per_environment feature flag,
which is safe to enable/disable at any time.
When Kubernetes clusters were originally built they could only
exist at the project level, and so there was logic included
that assumed there would only ever be a single Kubernetes
namespace per cluster. We now support clusters at the group
and instance level, which allows multiple namespaces.
This change consolidates various project-specific fallbacks to
generate namespaces, and hands all responsibility to the
Clusters::KubernetesNamespace model. There is now no concept of
a single namespace for a Clusters::Platforms::Kubernetes; to
retrieve a namespace a project must now be supplied in all cases.
This simplifies upcoming work to use a separate Kubernetes
namespace per project environment (instead of a namespace
per project).
