MINOR: Cleanup JMH-Benchmarks Module

[sjhajharia]

Now that Kafka supports Java 17, this PR makes some changes in
jmh-benchmarks module. The changes mostly include:

• Collections.emptyList(), Collections.singletonList() and
  Arrays.asList() are replaced with List.of()
• Collections.emptyMap() and Collections.singletonMap() are replaced
  with Map.of()
• Collections.singleton() is replaced with Set.of()

[Yunyung]

Thanks for the PR. Could you also do this cleanup?
Collections.unmodifiableMap -> Map.copyOf

[sjhajharia]

Thanks @Yunyung for the review. I have addressed the comment.
PTAL when possible!

[m1a2st]

Thanks @sjhajharia for this patch, left a comment

[m1a2st]

this mkMapOfPartitionRacks method is unused, we should remove it.

[Yunyung]

mkMapOfPartitionRacks will be removed all at once in #19797, so it's fine here.

[m1a2st]

Please resolve the conflict, thanks

[sjhajharia]

Hey @m1a2st
I have updated the PR

[m1a2st]

Thanks, LGTM

[sjhajharia]

cc: @frankvicky