fix(feature): preserves original target namespace (opendatahub-io#1148)

This change ensures that original target namespace is used when invoked
directly in the builder.

Typically subsequent calls of .TargetNamespace in the feature builder
indicate coding/copy-paste error and should be reduced to one.

However,in the FeatureHandler, where we group features together we do not have
to specify target namespace for each feature, as it is defaulted to the
one defined on the handler level. This is convenient, but limits
application of features to a single namespace, as the value is always
overwritten.

(cherry picked from commit a890ffa)

pkg/feature/builder.go

@@ -67,9 +67,11 @@ func (fb *featureBuilder) Source(source featurev1.Source) *featureBuilder {
 }
 
 // TargetNamespace sets the namespace in which the feature should be applied.
-// If not set, the feature will be applied in the application namespace.
+// Calling it multiple times in the builder chain will have no effect, as the first value is used.
 func (fb *featureBuilder) TargetNamespace(targetNs string) *featureBuilder {
-	fb.targetNs = targetNs
+	if fb.targetNs == "" {
+		fb.targetNs = targetNs
+	}
 
 	return fb
 }