By Elizabeth Piper LONDON (Reuters) -British Prime Minister Boris Johnson has promised to shake up operations in his 10 Downing Street office to try to survive his gravest crisis yet over boozy events held at the heart of power during COVID-19 lockdowns. Key to the organisational changes is a promise he made on Monday to lawmakers from his Conservative Party at a meeting in parliament to turn to Lynton Crosby, an Australian political strategist who has helped him before and is respected by many Conservative lawmakers, as an ad hoc “strategic adviser”. Johnson then reaffirmed his commitment to …