MOSCOW, Dec 6 (Reuters) - Russian President Vladimir Putin will meet Crown Prince Mohammed bin Salman in Saudi Arabia on Wednesday, during a rare trip abroad, to discuss oil production, OPEC+ and the wars in the Gaza Strip and Ukraine. Putin's meeting with the prince, known as MbS, comes after oil prices fell despite a pledge by OPEC+, which groups the Organization of the Petroleum Exporting Countries and allies led by Russia, to further cut output.