As found in #13965 (and as a follow-up to #13999), we also need to define what happens if both managedNamespaceMetadata and an Application manifest are defined for the same namespace.

The idea here is that if that happens, we emit an
ApplicationConditionRepeatedResourceWarning, and set the sync status to Unknown, since it's unclear what is supposed to happen. the managedNs doesn't get added to the list of targetObjs if there is already a source definition of the namespace.

Fixes #15815

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