[mqtt-to-kafka] Migrate akka dependencies to pekko

[laglangyue]

this pr inclueds:
Using pekko instead of akka in the document and code.
Using pekko-connectors style by https://github.com/apache/incubator-pekko-connectors/blob/main/.scalafmt.conf,because this module uses 4 spaces for indentation.
Test:
test local by docker 24.0.7 on Mint Linux 21
test failed,because missing mqtt container.

[laglangyue]

Due to the dependency of this sample on docker-compose.yml, testing is a bit cumbersome and cannot be completed directly by running the main function. I think it will improve the testing of Later