Removes junit 4 dependency

[codefromthecrypt]

This changes to the next minor so that we can remove the junit 4 compile dependency. To do so, this ports all tests to jupiter (v5) and stops publishing zipkin-junit (v4).

The plan is to cut a new version without any changes to the main tree. This will allow a cleaner cutover for server extensions who can first move to the latest patch, and subsequently the next minor. Specifically, this is for zipkin-gcp and zipkin-aws and I personally will handle this.

Note: Certain test libraries, notably testcontainers and activemq-junit have an indirect dependency on old junit. However, we don't re-export that in our zipkin-tests or zipkin-junit5 modules.

While I had to do some manual work, I had a lot of help from openrewrite. Here's the part that helped a lot.

$ ./mvnw -U org.openrewrite.maven:rewrite-maven-plugin:run \
  -Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-testing-frameworks:LATEST \
  -Drewrite.activeRecipes=org.openrewrite.java.testing.junit5.JUnit4to5Migration

[codefromthecrypt]

manually verified also, since there are a lot of lines.

$ ag 'import .*junit.' --java --noheading |grep -v '^\s*$' | wc -l
     352
$ ag 'import .*junit.' --java --noheading |egrep -v '(^\s*$|junit5|jupiter)'
zipkin-collector/activemq/src/test/java/zipkin2/collector/activemq/ITActiveMQCollector.java:27:import org.apache.activemq.junit.EmbeddedActiveMQBroker;

[anuraaga]

.

[anuraaga]

Skimmed through a few files for kicks but this is probably the main change and if build is green then it looks like it worked well

[timtebeek]

Might be worth to followup with these AssertJ best practices once this is merged, or cherry pick that into here:
master...timtebeek:zipkin:refactor/assertj-best-practices

[codefromthecrypt]

Thanks @timtebeek I'll create a PR off your changes next.

[timtebeek]

I'm seeing there's conflicts; would you want me to recreate the changes? That's trivial with the platform we have.

[codefromthecrypt]

added #3630 and will cut the minor afterwards