Add option to set container's default to empty container #979

Job	Run time
Build sbt/Scala client, servers (samples/server/petstore/scala-play-server)	4m 48s
Build sbt/Scala client, servers (samples/client/petstore/scala-pekko)	49s
Build sbt/Scala client, servers (samples/server/petstore/scala-akka-http-server)	52s
Build sbt/Scala client, servers (samples/client/petstore/scala-http4s)	50s
Build sbt/Scala client, servers (samples/client/petstore/java/okhttp-gson)	44s
Build sbt/Scala client, servers (samples/client/petstore/scalaz)	1m 5s
Build sbt/Scala client, servers (samples/server/petstore/scala-lagom-server)	4m 15s
Build sbt/Scala client, servers (samples/server/petstore/scala-pekko-http-server)	55s
Build sbt/Scala client, servers (samples/server/petstore/scalatra)	58s
Build sbt/Scala client, servers (samples/server/petstore/scala-cask)	1m 23s
Build sbt/Scala client, servers (samples/server/petstore/scala-http4s-server)	1m 0s
	17m 39s

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