Synthesis of a S‐(Carboxymethyl)cysteine Analog of (L‐2‐Amino‐6‐adipyl)‐L‐cysteinyl‐D‐valine and its Cell Free Biosynthetic Conversion into 6‐[2‐(D‐2‐Amino‐2‐carboxyethyl)thio) acetamido]penicillanic Acid