dockerimg: pass -x flag to inner sketch to enable experimental features

The -x flag needs to be passed from the outer sketch process to the inner sketch process
to ensure experimental features are correctly enabled across both processes.

Co-Authored-By: sketch <hello@sketch.dev>
diff --git a/dockerimg/dockerimg.go b/dockerimg/dockerimg.go
index 7aecb16..a4c82bc 100644
--- a/dockerimg/dockerimg.go
+++ b/dockerimg/dockerimg.go
@@ -97,6 +97,9 @@
 
 	// DockerArgs are additional arguments to pass to the docker create command
 	DockerArgs string
+
+	// ExperimentFlag contains the experimental features to enable
+	ExperimentFlag string
 }
 
 // LaunchContainer creates a docker container for a project, installs sketch and opens a connection to it.
@@ -468,6 +471,7 @@
 		"-outside-os="+config.OutsideOS,
 		"-outside-working-dir="+config.OutsideWorkingDir,
 		"-open=false",
+		"-x="+config.ExperimentFlag,
 	)
 	if config.Model != "" {
 		cmdArgs = append(cmdArgs, "-model="+config.Model)