Allow -Pdocker-platform during distDocker (#4828)

As an example of usecase - this should make it easier to build linux/amd64 images on M1.

Signed-off-by: Jiri Peinlich <jiri.peinlich@gmail.com>

Signed-off-by: Jiri Peinlich <jiri.peinlich@gmail.com>
Co-authored-by: Sally MacFarlane <macfarla.github@gmail.com>

build.gradle

@@ -649,9 +649,14 @@ task distDocker {
       }
       exec {
         def image = "${dockerImageName}:${dockerBuildVersion}-${jvmVariant}"
+        def dockerPlatform = ""
+        if (project.hasProperty('docker-platform')){
+          dockerPlatform = "--platform ${project.getProperty('docker-platform')}"
+          println "Building for platform ${project.getProperty('docker-platform')}"
+        }
         executable "sh"
         workingDir dockerBuildDir
-        args "-c", "docker build --build-arg BUILD_DATE=${buildTime()} --build-arg VERSION=${dockerBuildVersion} --build-arg VCS_REF=${getCheckedOutGitCommitHash()} -t ${image} ."
+        args "-c", "docker build ${dockerPlatform} --build-arg BUILD_DATE=${buildTime()} --build-arg VERSION=${dockerBuildVersion} --build-arg VCS_REF=${getCheckedOutGitCommitHash()} -t ${image} ."
       }
     }