[nixpacks] enable docker buildx

Author: tsirysndr

nixpacks/src/dagger/lib.ts

@@ -23,10 +23,15 @@ export const getDirectory = async (
 };
 
 export const docker = (version = "24.0", cached = false) => {
+  const buildx = dag.container().from("docker/buildx-bin").file("/buildx");
   let ctr = dag
     .container()
     .from(`docker:${version}-dind`)
+    .withEnvVariable("DOCKER_CLI_EXPERIMENTAL", "enabled")
     .withoutEntrypoint()
+    .withExec(["mkdir", "-p", "/usr/libexec/docker/cli-plugins"])
+    .withFile("/usr/libexec/docker/cli-plugins/docker-buildx", buildx)
+    .withExec(["docker", "buildx", "version"])
     .withExposedPort(2375);
 
   if (cached) {