[docs] clarify steps exempt for Serverless deployment in CLI branch d…

…eployment (#23430)

## Summary & Motivation
Doc: [Using Branch Deployments (CI) with the dagster-cloud
CLI](https://docs.dagster.io/dagster-plus/managing-deployments/branch-deployments/using-branch-deployments#using-branch-deployments-ci-with-the-dagster-cloud-cli
)

Doc is Hybrid-centric so Serverless deployment users can be confused in
some steps

## How I Tested These Changes
👀

docs/content/dagster-plus/managing-deployments/branch-deployments/using-branch-deployments.mdx

@@ -25,8 +25,8 @@ Utilizing Branch Deployments requires setting up two components: the Branch Depl
 
 - **Organization Admin** permissions in Dagster+
 - To install the [`dagster-cloud` CLI](/dagster-plus/managing-deployments/dagster-plus-cli)
-- The ability to run a new agent in your infrastructure
 - The ability to configure your CI platform
+- The ability to run a new agent in your infrastructure. This isn't required if you're using [Serverless deployment](/dagster-plus/deployment/serverless).
 
 ---
 
@@ -38,6 +38,14 @@ Utilizing Branch Deployments requires setting up two components: the Branch Depl
 
 ## Step 2: Create and configure an agent
 
+<Note>
+  If you're using Serverless deployment, this step isn't required.{" "}
+  <a href="#step-3-create-a-branch-deployment-using-the-dagster-cloud-cli">
+    Skip to Step 3
+  </a>
+  .
+</Note>
+
 <BDCreateConfigureAgent />
 
 ---