By Michael Holden LONDON (Reuters) -The wife of Julian Assange vowed to fight using every possible legal avenue after British Home Secretary Priti Patel on Friday approved the WikiLeaks’ founder’s extradition to the United States to face criminal charges. Assange is wanted by U.S. authorities on 18 counts, including a spying charge, relating to WikiLeaks’ release of vast troves of confidential U.S. military records and diplomatic cables which Washington said had put lives in danger. His supporters say he is an anti-establishment hero who has been victimised because he exposed U.S. wrongdoing i…