feat(process): honor cluster-wide for k8s default objects (#320)

No longer attaches namespaces to known cluster-wide objects. This is done by maintaining a static list of those in the source code. This is limited to those objects included in a clean, stock install of the latest Kubernetes version. 
For CRDs, the annotation must be used.

docs/docs/namespaces.md

@@ -31,12 +31,13 @@ legit cases where it's handy to have them span multiple namespaces, for example:
 
 Some resources in Kubernetes are cluster-wide, meaning they don't belong to a single namespace at all.
 
-To Tanka these appear as _Scenario 1 (see above)_, so it will set the default
-namespace. In reality however, this is **not a problem**, because `kubectl`
-discards this information silently. We made this design-choice, because it
-simplifies our code a lot.
+Tanka will make an attempt to not add namespaces to *known* cluster-wide types. 
+It does this with a short list of types in [the source code](https://github.com/grafana/tanka/blob/master/pkg/process/namespace.go).
 
-In case this ever becomes a problem, you can **override this** behavior
+Tanka cannot feasably maintain this list for all known custom resource types. In those cases, resources will have namespaces added to their manifests,
+and kubectl should happily apply them as non-namespaced resources.
+
+If this presents a problem for your workflow, you can **override this** behavior
 per-resource, by setting the `tanka.dev/namespaced` annotation to `"false"`
 (must be of `string` type):
 

pkg/process/namespace.go

@@ -10,6 +10,36 @@ const (
 	AnnotationNamespaced = MetadataPrefix + "/namespaced"
 )
 
+// This is a list of "cluster-wide" resources harvested from `kubectl api-resources --namespaced=false`
+// This helps us to know which objects we should NOT apply namespaces to automatically.
+// We can add to this list periodically if new types are added.
+// This only applies to built-in kubernetes types. CRDs will need to be handled with annotations.
+var clusterWideKinds = map[string]bool{
+	"APIService":                     true,
+	"CertificateSigningRequest":      true,
+	"ClusterRole":                    true,
+	"ClusterRoleBinding":             true,
+	"ComponentStatus":                true,
+	"CSIDriver":                      true,
+	"CSINode":                        true,
+	"CustomResourceDefinition":       true,
+	"MutatingWebhookConfiguration":   true,
+	"Namespace":                      true,
+	"Node":                           true,
+	"NodeMetrics":                    true,
+	"PersistentVolume":               true,
+	"PodSecurityPolicy":              true,
+	"PriorityClass":                  true,
+	"RuntimeClass":                   true,
+	"SelfSubjectAccessReview":        true,
+	"SelfSubjectRulesReview":         true,
+	"StorageClass":                   true,
+	"SubjectAccessReview":            true,
+	"TokenReview":                    true,
+	"ValidatingWebhookConfiguration": true,
+	"VolumeAttachment":               true,
+}
+
 // Namespace injects the default namespace of the environment into each
 // resources, that does not already define one. AnnotationNamespaced can be used
 // to disable this per resource
@@ -20,7 +50,9 @@ func Namespace(list manifest.List, def string) manifest.List {
 
 	for i, m := range list {
 		namespaced := true
-
+		if clusterWideKinds[m.Kind()] {
+			namespaced = false
+		}
 		// check for annotation override
 		if s, ok := m.Metadata().Annotations()[AnnotationNamespaced]; ok {
 			namespaced = s == "true"