Migrate JUnit asserts to AssertJ

AssertJ provides a rich set of assertions, truly helpful error messages, improves test code readability. Converts assertions from org.junit.jupiter.api.Assertions to org.assertj.core.api.Assertions. Will convert JUnit 4 to JUnit Jupiter if necessary to match and modify assertions.

• Issue #17047: Migrate JUnit asserts to AssertJ #17048
• checkers issues: LocalVariableName #17049
• [POC] Migrate JUnit asserts to AssertJ - impl apache/maven#2307
• https://docs.openrewrite.org/recipes/java/testing/assertj/junittoassertj