Defense Secretary Lloyd J. Austin III presented himself before a congressional committee for chastisement on Thursday, continuing a round of mea culpas over his failure last month to tell his boss that he was in the hospital with complications from prostate cancer surgery.Republican lawmakers had been preparing to lay into Mr. Austin before the hearing, calling former Defense Department officials for advice. Even the formal title of the hearing, listed on the House Armed Services Committee’s website, struck an ominous tone: “A Review of Defense Secretary Austin’s Unannounced…