Water‐Soluble Cobalt(II) and Copper(II) Complexes of 3‐(5‐Chloro‐2‐hydroxy‐3‐sulfophenylhydrazo)pentane‐2,4‐dione as Building Blocks for 3D Supramolecular Networks and Catalysts for TEMPO‐Mediated Aerobic Oxidation of Benzylic Alcohols