Warn when /status subresource is not enabled

[mgruener]

Metacontroller assumes that a parent resource always has the /status subresource enabled, which it is not by default (at least for CRDs). As Metacontroller also always adds the .status.observedGeneration field, this leads to a hot-loop where adding the .status.observedGeneration field leads to an increment of the .metadata.generation field.

It would be nice when Metacontroller either logs an error when the /status subresource is disabled for a parent resource or does not add the .status.observedGeneration field in this case.