LONDON (Reuters) – British Prime Minister Boris Johnson, who said on Thursday he would resign, is due to throw a big wedding party to mark his marriage to wife Carrie at his official Chequers country residence later this month, the Mirror reported. Johnson, who will remain leader until a new prime minister is chosen, is staying on in part to throw the “lavish” party, the Mirror reported, citing unnamed senior sources from Johnson’s Conservative Party. Asked about the report, a Downing Street spokesperson said: “The Prime Minister has a strong sense of duty and will continue to serve his countr…