It was a mutual admiration society at the Cambridge PD Tuesday as best-selling author Patricia Cornwell and Police Commissioner Robert Haas patted each other on the back. Cornwell, who lives in a bedroom community west of Boston these days, was given an engraved crystal plaque for her generous financial donations to the police department, and in return she handed Haas a signed copy of her latest novel, “The Bone Bed,” which is set in the Peoples’ Republic of Cambridge and references the PD. As any faithful Cornwell reader will tell you, the author’s fearless character, Dr. Kay Scarpetta, moved to Boston from the Big Apple a while ago. As a result, the Cambridge cop shop is now featured prominently in her books. Cornwell has sold over 100 million copies of her books worldwide.