Add on_fit_epoch_end callback (#5232)

* Add `on_fit_epoch_end` callback

* Add results to train

* Update __init__.py

utils/loggers/__init__.py

@@ -131,7 +131,7 @@ class Loggers():
             if ((epoch + 1) % self.opt.save_period == 0 and not final_epoch) and self.opt.save_period != -1:
                 self.wandb.log_model(last.parent, self.opt, epoch, fi, best_model=best_fitness == fi)
 
-    def on_train_end(self, last, best, plots, epoch):
+    def on_train_end(self, last, best, plots, epoch, results):
         # Callback runs on training end
         if plots:
             plot_results(file=self.save_dir / 'results.csv')  # save results.png