[breaking] [jvm-packages] Remove rabit check point. (#9599)

- Add `numBoostedRound` to jvm packages
- Remove rabit checkpoint version.
- Change the starting version of training continuation in JVM [breaking].
- Redefine the checkpoint version policy in jvm package. [breaking]
- Rename the Python check point callback parameter. [breaking]
- Unifies the checkpoint policy between Python and JVM.

tests/test_distributed/test_with_dask/test_with_dask.py

@@ -2238,7 +2238,7 @@ class TestDaskCallbacks:
                 y,
                 callbacks=[
                     xgb.callback.TrainingCheckPoint(
-                        directory=Path(tmpdir), iterations=1, name="model"
+                        directory=Path(tmpdir), interval=1, name="model"
                     )
                 ],
             )