Put test assertion errors on multiple lines

[barbeque-squared]

Enhancement Description

Put test failure messages (at least org.axonframework.test.AxonAssertionError, but there's probably more: search the codebase for "but got") on separate lines. This doesn't really matter for something simple like an integer, but when it starts printing events with half a dozen or so fields, this would make it much easier to debug.

This happens at least when something is failing in AggregateTestFixture's expectEvents method. Maybe some of the places the above search query returns don't need this, and maybe there's other places, but I'm fine with incremental improvements.

Current/Wanted behaviour examples are adapted from a real test I was working on, just the field names and contents have been scrubbed a bit.

Current Behaviour

org.axonframework.test.AxonAssertionError: One of the messages contained a different payload than expected

The message of type [MyAwesomeEvent] was not as expected.
Expected <MyAwesomeEvent(someIdentifier=awesomeId, anotherId=example, name=facts.doc, description=Axon is really awesome, version=1.0, hierarchy1=null, hierarchy2=null, hierarchy3=null, uploadedBy=uploadedBy, uploadedAt=2023-06-16T08:10:12.713542187, userType=USER, year=2023)> but got <MyAwesomeEvent(someIdentifier=awesomeId, anotherId=example, name=facts.doc, description=null, version=null, hierarchy1=null, hierarchy2=null, hierarchy3=null, uploadedBy=, uploadedAt=2023-06-16T08:10:12.713542187, userType=USER, year=2023)>

Wanted Behaviour

org.axonframework.test.AxonAssertionError: One of the messages contained a different payload than expected

The message of type [MyAwesomeEvent] was not as expected.
Expected <MyAwesomeEvent(someIdentifier=awesomeId, anotherId=example, name=facts.doc, description=Axon is really awesome, version=1.0, hierarchy1=null, hierarchy2=null, hierarchy3=null, uploadedBy=uploadedBy, uploadedAt=2023-06-16T08:10:12.713542187, userType=USER, year=2023)>
 but got <MyAwesomeEvent(someIdentifier=awesomeId, anotherId=example, name=facts.doc, description=null, version=null, hierarchy1=null, hierarchy2=null, hierarchy3=null, uploadedBy=, uploadedAt=2023-06-16T08:10:12.713542187, userType=USER, year=2023)>

Notice how it's immediately and trivially clear that description is the first field it's failing on.

Possible Workarounds

Copy pasting the test output into an editor and adding a newline manually (this is what I currently do)

[smcvb]

Simple adjustment to make, I like it. As I'm finalizing 4.8.0, I think it makes sense to fit this in.