By Valerie Volcovici and Nandita Bose WASHINGTON (Reuters) -President Joe Biden and first lady Jill Biden on Saturday announced the passing of their German shepherd Champ, who they called a “constant, cherished companion” for 13 years. “In our most joyful moments and in our most grief-stricken days, he was there with us, sensitive to our every unspoken feeling and emotion. We love our sweet, good boy and will miss him always,” the Bidens said in a statement. Champ was one of two German shepherds living at the White House with the president and first lady. Biden got Champ in 2008, the year he w…