By Steve Holland, Idrees Ali and Phil Stewart WASHINGTON (Reuters) -U.S. President Joe Biden did not learn that his defense secretary, Lloyd Austin, had prostate cancer until Tuesday, the White House said, minutes after it was disclosed to the public along with an infection that was also kept under wraps. Austin, who is 70, has been hospitalized since Jan. 1 at Walter Reed National Military Medical Center — a fact that the Pentagon had kept from the public, the White House and Congress for much of last week, triggering a major political backlash. Austin’s own deputy, Kathleen Hicks, was also …