chore(sdk): Bring back kfp.v2.components as an alias to kfp.components (#5083)

* Bring back kfp.v2.components with a DeprecationWarning

* fix test

* no deprecation warning

sdk/python/kfp/v2/compiler/compiler_test.py

@@ -17,7 +17,7 @@ import shutil
 import tempfile
 import unittest
 
-from kfp import components
+from kfp.v2 import components
 from kfp.v2 import compiler
 from kfp.v2 import dsl
 

sdk/python/kfp/v2/components/__init__.py

@@ -0,0 +1,15 @@
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from kfp.components import *