By Elizabeth Piper and Muvija M LONDON (Reuters) -A “humbled” Boris Johnson said he took full responsibility but would not quit after a damning official report on Wednesday detailed a series of illegal lockdown parties at the British leader’s Downing Street office. Johnson has faced repeated calls to resign from opposition politicians and some in his own party over the alcohol-fuelled gatherings, after it was revealed that he and officials had broken COVID-19 rules that all but banned people from socialising outside their households. “I … am humbled and I have learned a lesson,” Prime Minist…