By Muvija M, Chavi Mehta and Aditya Soni LONDON (Reuters) -Microsoft’s partnership with ChatGPT maker OpenAI is under US and UK antitrust scrutiny, the British regulator and a media report said on Friday, following the startup’s boardroom battle that led to the sudden ouster and return of CEO Sam Altman. After the dramatic episode last month, Microsoft, a major OpenAI backer, was granted a non-voting, observer position at the company by a new three-member initial board. Microsoft’s representative can attend OpenAI’s board meetings and access confidential information, but cannot vote on matters…