By Andrew MacAskill LONDON (Reuters) – Prime Minister Rishi Sunak faces the most dangerous moment of his premiership this week, when he is due to appear before a COVID-19 inquiry and must win a crunch vote in parliament on his plan to revive a policy to send asylum seekers to Rwanda. Just over a year since he became prime minister, Sunak is struggling to maintain his authority, as politicians on both the left and the right of his Conservative Party are threatening to vote against his flagship asylum policy. Parliament will hold a first vote on Tuesday on the legislation that would override som…