By Maya Gebeily BAABDA, Lebanon (Reuters) – Michel Aoun, the 89-year-old Christian president who presided over Lebanon’s cataclysmic financial meltdown and the deadly Beirut port blast, vacates the presidential palace on Sunday, leaving a void at the top of the failing Lebanese state. Lebanon’s parliament has so far been unable to agree on a successor in the role, which has the power to sign bills into law, appoint new prime ministers and green-light government formations before they are voted on by parliament. Like during more than half of Aoun’s time in office, Lebanon is currently governed …