Add scalafmt plugin to scala-pekko client generator (#23362) #43

Job	Run time
Build sbt/Scala (samples/client/petstore/scala-pekko)	1m 2s
Build sbt/Scala (samples/client/petstore/scala-sttp4)	1m 5s
Build sbt/Scala (samples/client/petstore/scalaz)	1m 4s
Build sbt/Scala (samples/client/petstore/scala-http4s)	1m 7s
Build sbt/Scala (samples/client/petstore/scala-sttp-circe)	1m 0s
Build sbt/Scala (samples/client/petstore/scala-sttp)	1m 8s
Build sbt/Scala (samples/client/petstore/scala-sttp4-jsoniter)	1m 0s
Build sbt/Scala (samples/client/petstore/scala-akka)	1m 17s
	8m 43s

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