Allow empty namespace for fission function and builder (#2621)

Currently, we create Fission resources in the default namespace, function-related resources are created in the fission-function namespace, whereas builder resources are created in the fission-builder namespace. This causes confusion for a lot of users.
In this fix, we allow the user to set the function and builder namespace empty so that function and builder resources are created in the same namespace as the function resource always.

If the user desires older behaviour they can functionNamespace and builderNamespace the same previous before the upgrade.

* use default namespace for fission  function and builder
* support for existing fission namespaces
* Replace builder and function namespace with template
* Fix namespace creation template

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/utils/namespace.go

@@ -0,0 +1,63 @@
+package utils
+
+import (
+	"os"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+const (
+	ENV_FUNCTION_NAMESPACE string = "FISSION_FUNCTION_NAMESPACE"
+	ENV_BUILDER_NAMESPACE  string = "FISSION_BUILDER_NAMESPACE"
+	ENV_DEFAULT_NAMESPACE  string = "FISSION_DEFAULT_NAMESPACE"
+)
+
+type NamespaceResolver struct {
+	FunctionNamespace string
+	BuiderNamespace   string
+	DefaultNamespace  string
+}
+
+var nsResolver *NamespaceResolver
+
+func init() {
+	nsResolver = &NamespaceResolver{
+		FunctionNamespace: os.Getenv(ENV_FUNCTION_NAMESPACE),
+		BuiderNamespace:   os.Getenv(ENV_BUILDER_NAMESPACE),
+		DefaultNamespace:  os.Getenv(ENV_DEFAULT_NAMESPACE),
+	}
+}
+
+func (nsr *NamespaceResolver) GetBuilderNS(namespace string) string {
+	if nsr.FunctionNamespace == "" || nsr.BuiderNamespace == "" {
+		return namespace
+	}
+
+	if namespace != metav1.NamespaceDefault {
+		return namespace
+	}
+	return nsr.BuiderNamespace
+}
+
+func (nsr *NamespaceResolver) GetFunctionNS(namespace string) string {
+	if nsr.FunctionNamespace == "" || nsr.BuiderNamespace == "" {
+		return namespace
+	}
+
+	if namespace != metav1.NamespaceDefault {
+		return namespace
+	}
+	return nsr.FunctionNamespace
+}
+
+func (nsr *NamespaceResolver) ResolveNamespace(namespace string) string {
+	if nsr.FunctionNamespace == "" || nsr.BuiderNamespace == "" {
+		return nsr.DefaultNamespace
+	}
+	return namespace
+}
+
+// GetFissionNamespaces => return all fission core component namespaces
+func DefaultNSResolver() *NamespaceResolver {
+	return nsResolver
+}