By Guy Faulconbridge LONDON (Reuters) – President Vladimir Putin will send a “doomsday” warning to the West when he leads celebrations on Monday marking the 77th anniversary of the Soviet Union’s victory over Nazi Germany, brandishing Russia’s vast firepower while its forces fight on in Ukraine. Defiant in the face of deep Western isolation since he ordered the invasion of Russia’s neighbour, Putin will speak on Red Square before a parade of troops, tanks, rockets and intercontinental ballistic missiles. A fly-past over St Basil’s Cathedral will include supersonic fighters, Tu-160 strategic bo…