Add scalafmt plugin to scala-http4s-server generator (#23458) #27

Job	Run time
Build sbt/Scala (samples/server/petstore/scala-play-server)	6m 57s
Build sbt/Scala (samples/server/petstore/scalatra)	4m 27s
Build sbt/Scala (samples/server/petstore/scala-akka-http-server)	58s
Build sbt/Scala (samples/server/petstore/scala-pekko-http-server)	54s
Build sbt/Scala (samples/server/petstore/scala-http4s-server)	1m 1s
Build sbt/Scala (samples/server/petstore/scala-cask)	1m 28s
	15m 45s

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