[Reviewers wanted for two PR's] 1) SLF4J version upgrade and 2) various minor version updates

[Dejan Stojadinović]

Hi all,

Feel free to review these PR's:

   1. https://github.com/apache/kafka/pull/21290 KAFKA-20061 slf4j-api
   version upgrade: 1 -->> 2 (also: log4j-slf4j-impl artifact is renamed to
   log4j-slf4j2-impl)
   2. https://github.com/apache/kafka/pull/21295 MINOR: buildscript and
   project dependencies version updates

Regards,
Dejan https://github.com/dejan2609