SAUDI Arabia is preparing to open its first alcohol store in the capital Riyadh which will serve exclusively non-Muslim diplomats, according to a source familiar with the plans and a document. Customers will have to register via a mobile app, get a clearance code from the foreign ministry, and respect monthly quotas with their purchases, said the document, which was seen by Reuters. The move is a milestone in the kingdom's efforts, led by Saudi Crown Prince Mohammed bin Salman, to open the ultra-conservative Muslim country for tourism and business as drinking alcohol is forbidden in Islam. It is also…