Support --pull option for docker build

[sideisra]

We would like to update ur base images at every build to keep track with the releases. Therefore we would like to use the --pull option of the docker build command.

There should be an option for the build task to enable the --pull docker option. Like that:

deploy {
    default{
       dockerBuild { 
          prepareTask = "prepareBuildDocker" // task the copies all needed files to build/buildDocker
          version = "0.0.1" // if not set gradle project version "-$timestamp" is used
          architecture = "linux/amd64" // if not set docker default architecture is chosen
          pullNewerImages = true
       }
    }
}