[#4970] Change MessageTest unit tests to deterministic implementation

[anthonyx24]

Issue: This is the same issue as #4946 involving JSON comparisons. Here it's happening in both the should_encode_register_type and should_encode_unregister_type unit tests. In summary, since JSONs are unordered, after converting them to strings, the parameter ordering is not guaranteed, which can lead to the tests failing occasionally. For another example of this issue being addressed, see this previous merged PR.

These two tests were flagged via the NonDex tool, which detects potentially unreliable tests due to underlying Java API assumptions. To see the Nondex output for the test class MessageTest, you can run:

mvn -pl service-registry/registry-lightweight edu.illinois:nondex-maven-plugin:2.1.7:nondex -Dtest="org.apache.servicecomb.registry.lightweight.MessageTest"

Fix: The fix here is also similar to the one I detailed in this PR for the other issue: #4947. I use JSONAssert's assertEquals() method, using non-strict checking (which ignores parameter ordering). This compares the JSON strings without enforcing parameter ordering, which removes the potentially unreliable nature of these tests. This library is already included within the spring-boot dependency, which is already used in the project, so there's no need to update the pom file. Rerunning Nondex shows a passing result.

Since JSONAssert.assertEquals can throw a JsonException, I wrap the code blocks in a try-catch, then using Assertions.fail() to fail the unit test if an exception occurs. I'm catching the generic Exception to handle all possible exceptions, but let me know if I should change this. I'm also using AssertJ for this since the existing assertions in the class use AssertJ, but I can switch to jUnit as well if that's better.

PR Checklist:

• Github Issue: [BUG] - Nondeterminism in unit tests in MessageTest due to JSON parameter ordering #4970
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