March 27 (Reuters) - A giant recruitment advert for Russia's Wagner mercenary force has appeared on the facade of an office building next to a highway in north-east Moscow. Its boss Yevgeny Prigozhin, a 61-year-old ex-convict whose company grew wealthy by catering events and fulfilling contracts for the Kremlin and government ministries, said earlier in March that he aimed to recruit 30,000 new fighters by mid-May. See here for a complete list of exchanges and delays