add --push flag to buildx (#571)

Author: yiweny

readme.md

@@ -68,6 +68,8 @@ build/
 - `builder` (optional) a string argument which defines which builder buildx should use; defaults to `null`
 - `load` (optional) a boolean argument which defines whether Docker buildx builder should add --load flag,
   loading the image into the local repository; defaults to `false`
+- `push` (optional) a boolean argument which defines whether Docker buildx builder should add --push flag,
+  pushing the image into the remote registry; defaults to `false`
 
 To build a docker container, run the `docker` task. To push that container to a
 docker repository, run the `dockerPush` task.

src/main/groovy/com/palantir/gradle/docker/DockerExtension.groovy

@@ -45,6 +45,7 @@ class DockerExtension {
     private boolean buildx = false
     private Set<String> platform = ImmutableSet.of()
     private boolean load = false
+    private boolean push = false
     private String builder = null
 
     private File resolvedDockerfile = null
@@ -188,6 +189,14 @@ class DockerExtension {
         this.pull = pull
     }
 
+    public boolean getPush() {
+	return push
+    }
+
+    public void push(boolean push) {
+	this.push = push
+    }
+
     boolean getBuildx() {
         return buildx
     }

src/main/groovy/com/palantir/gradle/docker/PalantirDockerPlugin.groovy

@@ -181,6 +181,12 @@ class PalantirDockerPlugin implements Plugin<Project> {
             if (ext.load) {
                 buildCommandLine.add '--load'
             }
+	    if (ext.push) {
+	        buildCommandLine.add '--push'
+	    	if (ext.load) {
+    		    throw new Exception("cannot combine 'push' and 'load' options")
+	    	}
+	    }
             if (ext.builder != null) {
                 buildCommandLine.addAll('--builder', ext.builder)
             }