Cannot disable Http Port

Gradle play plugin does not have ability to disable http port

**Expected Behavior**
Play (SBT) allows user to disable http port by passing the -Dhttp.port=disabled option (See: [https://www.playframework.com/documentation/2.6.x/ConfiguringHttps#Turning-HTTP-off](https://www.playframework.com/documentation/2.6.x/ConfiguringHttps#Turning-HTTP-off)).

**Current Behavior**
Current Gradle play plugin only takes Integer as the http.port number. (See: [PlayRunAdapterV24X](https://github.com/gradle/playframework/blob/master/src/main/java/org/gradle/playframework/tools/internal/run/PlayRunAdapterV24X.java#L11) and [PlayRunAdapterV26X](https://github.com/gradle/playframework/blob/master/src/main/java/org/gradle/playframework/tools/internal/run/PlayRunAdapterV26X.java#L11)).

In both implementation, play.core.server.DevServerStart.mainDevHttpMode method is used to start the play server.

If you look at play's [DevServerStart](https://www.playframework.com/documentation/2.4.2/api/scala/play/core/server/DevServerStart$.html) api, it actually has one more method called mainDevOnlyHttpsMode which can be used to start play server in HTTPS only mode. You can see how this is done in play's [Reloader](https://github.com/playframework/playframework/blob/8793cfaa568f79e822cb11c1d6a156331ca9ba74/framework/src/run-support/src/main/scala/play/runsupport/Reloader.scala#L230).

**Your Environment**
Play: 2.4 (the issue is applicable to later version)