chore: import upstream snapshot with attribution

tests/python/all-platform-minimal-test/README.md

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+<!--- Licensed to the Apache Software Foundation (ASF) under one -->
+<!--- or more contributor license agreements.  See the NOTICE file -->
+<!--- distributed with this work for additional information -->
+<!--- regarding copyright ownership.  The ASF licenses this file -->
+<!--- to you 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. -->
+
+# Core Cross Platform Regression Tests
+
+CI Unit test cases that will run on all platforms.
+To reduce the CI burden, we only put in test-cases that are platform sensitive.
+Please use the following guideline:
+
+- Always consider add tests to the unittest folder first.
+- If a problems that passes the Linux pipeline but fails in Windows or MacOS,
+  we should isolate the problem, write a minimal regression test case
+  and add it to this folder.
+- A test case in this folder should be minimal and finish in a reasonable amount of time.
+- Document about why it should be in the all-platform-minimal-test.