Convert kafka-clients unit test from groovy to java

[cuichenli]

No description provided.

[mateuszrzeszutek]

I left a couple of comments, they're mostly about minor style issues. Overall it looks great, thanks @cuichenli !

[mateuszrzeszutek]

The waitAndAssertTraces() method already waits for 1 completed trace, there should be no need to call waitForTraces() explicitly

Suggested change

	testing.waitForTraces(1);
	testing.waitAndAssertTraces(
	testing.waitAndAssertTraces(

[cuichenli]

removed most testing.waitForTraces but kept two where there is no testing.waitAndAssertTraces

[cuichenli]

@mateuszrzeszutek thanks for your comments, updated accordingly. please take a look again. thanks!

[mateuszrzeszutek]

Thanks @cuichenli !

[mateuszrzeszutek]

The latest dep version tests are failing against an errorprone warning

/home/runner/work/opentelemetry-java-instrumentation/opentelemetry-java-instrumentation/instrumentation/kafka/kafka-clients/kafka-clients-0.11/javaagent/src/test/java/io/opentelemetry/instrumentation/kafkaclients/KafkaClientDefaultTest.java:74: warning: [PreferJavaTimeOverload] If the numeric primitive (Duration.ofSeconds(5).toMillis()) represents a Duration, please call consumer.poll(Duration) instead.
    ConsumerRecords<?, ?> records = consumer.poll(Duration.ofSeconds(5).toMillis());
                                                 ^
    (see https://errorprone.info/bugpattern/PreferJavaTimeOverload)

You might want to add @SuppressWarnings("PreferJavaTimeOverload") whenever poll(long) is called

[cuichenli]

@mateuszrzeszutek thanks, all the tests passed