By Michael Holden and Kate Holton LONDON (Reuters) – Britain celebrates the second day of Queen Elizabeth’s Platinum Jubilee on Friday, with the highlight a service of thanksgiving attended by senior royals and politicians that the 96-year-old monarch herself will miss due to ongoing mobility issues. The four days of events kicked off on Thursday, when a happy-looking Elizabeth waved to crowds from the balcony of Buckingham Palace after a military parade and Royal Air Force flypast, and later led the lighting of the Principal Platinum Jubilee Beacon at her Windsor Castle home. The celebrations…