(v2) Improvements to the wandb integration (#4324)

* Improvements to the wandb integration

* small reorg + no global necessary

* feat(trainer): log epoch and final metrics

* Simplify logging a bit

* Fixup

* Fix crash when just running eval

Co-authored-by: Chris Van Pelt <vanpelt@gmail.com>
Co-authored-by: Boris Dayma <boris.dayma@gmail.com>

examples/test_examples.py

@@ -72,7 +72,7 @@ class ExamplesTests(unittest.TestCase):
             """.split()
         with patch.object(sys, "argv", testargs):
             result = run_glue.main()
-            del result["loss"]
+            del result["eval_loss"]
             for value in result.values():
                 self.assertGreaterEqual(value, 0.75)