Add support for custom platform (#32)

kaniko.go

@@ -30,6 +30,7 @@ type (
 		DigestFile    string   // Digest file location
 		NoPush        bool     // Set this flag if you only want to build the image, without pushing to a registry
 		Verbosity     string   // Log level
+		Platform      string   // Allows to build with another default platform than the host, similarly to docker build --platform
 	}
 
 	// Artifact defines content of artifact file
@@ -157,6 +158,10 @@ func (p Plugin) Exec() error {
 		cmdArgs = append(cmdArgs, fmt.Sprintf("--verbosity=%s", p.Build.Verbosity))
 	}
 
+	if p.Build.Platform != "" {
+		cmdArgs = append(cmdArgs, fmt.Sprintf("--customPlatform=%s", p.Build.Platform))
+	}
+
 	cmd := exec.Command("/kaniko/executor", cmdArgs...)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr