feat: use env var in pipeline snippet (#275)

Because

- #274

This commit

- use env var in pipeline snippet (close #274)

src/pages/pipelines/[id].tsx

@@ -42,7 +42,7 @@ export const getServerSideProps: GetServerSideProps = async (context) => {
     `${context.params?.id}`
   );
 
-  const snippet = `curl -X POST http://localhost:8081/v1alpha/pipelines/${context.params?.id}:trigger -d '{
+  const snippet = `curl -X POST ${process.env.PIPELINE_BACKEND_BASE_URL}/v1alpha/pipelines/${context.params?.id}:trigger -d '{
     "inputs": [
       {
         "image_url": "https://artifacts.instill.tech/imgs/dog.jpg"