docs: @RequirePOST
      public void doUpgrade(StaplerResponse rsp) throws IOException, ServletException {
          HudsonUpgradeJob job = new HudsonUpgradeJob(getCoreSource(), Jenkins.getAuthentication());
          if(!Lifecycle.get().canRewriteHudsonWar()) {
              sendError("Jenkins upgrade not supported in this running mode");
              return;
          }
  
          LOGGER.info("Scheduling the core upgrade");
          addJob(job);
          rsp.sendRedirect2(".");
      }