Use xmlunit-legacy instead of xmlunit

[puskarpeter]

• xmlunit is not compatible with JUnit5 hence we need to migrate it

What's changed?

Package migration for xmlunit, no code changes since xmlunit-legacy provides compatibility between versions 2.x and 1.x

What's your motivation?

JUnit5 compatibility. XMLUnit 1.6 would not compile, XMLUnit legacy everything works with JUnit5 as expected.

Anything in particular you'd like reviewers to focus on?

Anyone you would like to review specifically?

Have you considered any alternatives or workarounds?

Any additional context

https://github.com/xmlunit/xmlunit/#requirements

Checklist

• I've added unit tests to cover both positive and negative cases
• I've added the license header to any new files through ./gradlew licenseFormat
• I've used the IntelliJ auto-formatter on affected files
• I've updated the documentation (if applicable)

[timtebeek]

Thanks a lot @puskarpeter