exp/metrics/params diff: Replaced Old/New with a_rev/b_rev (#6814)

* Replaced Old/New with a_rev/b_rev

* Fixed tests

tests/unit/command/test_metrics.py

@@ -47,6 +47,8 @@ def test_metrics_diff(dvc, mocker, capsys):
         precision=5,
         markdown=True,
         round_digits=True,
+        a_rev="HEAD~10",
+        b_rev="HEAD~1",
     )
 
 

tests/unit/command/test_params.py

@@ -56,7 +56,13 @@ def test_params_diff_from_cli(dvc, mocker):
         deps=False,
     )
     show_diff_mock.assert_called_once_with(
-        {}, title="Param", markdown=False, no_path=False, show_changes=False
+        {},
+        title="Param",
+        markdown=False,
+        no_path=False,
+        show_changes=False,
+        a_rev=None,
+        b_rev=None,
     )