docs: update quickstart for new UI (#3062)

Updates federation quickstart to align with new Studio UI

docs/source/quickstart.mdx

@@ -38,7 +38,6 @@ To learn more about Apollo Federation and the benefits of using it with GraphOS,
 
 To complete this quickstart, you must have the following:
 
-- A [GraphOS Studio](https://studio.apollographql.com/?referrer=docs-content) account
 - A local version of Apollo's retail demo
   - Download or clone it from its [GitHub repository](https://github.com/apollosolutions/retail-supergraph)
 - The latest LTS version of [Node.js](https://nodejs.org/en)
@@ -441,9 +440,10 @@ In this step, you'll create an empty supergraph in GraphOS Studio and then publi
 
 #### Create supergraph
 
-1. Go to [studio.apollographql.com](https://studio.apollographql.com/?referrer=docs-content) and click **+ Create New Graph**.
-2. Enter a **Graph title**, for example `Federation Quickstart`. Leave the **Graph Architecture** as `Supergraph (Default)` and **Visible to Team Members** as `On`. Click **Next**.
-3. A **Publish your schema using Federation** dialog appears. Copy the entire example code block to a local text file using the copy button.
+1. If you don't yet have a [GraphOS Studio](https://studio.apollographql.com/?referrer=docs-content) account, create one now.
+2. If you're starting from a new Studio account, click **Connect a GraphQL API** when prompted. If working from an existing Studio account, click **+ Create New Graph** on the top right of the page.
+3. Enter a **Graph title**, for example `Federation Quickstart`. Leave the **Graph Architecture** as `Supergraph (Default)` and **Visible to Team Members** as `On`. Click **Next**.
+4. A **Publish your schema using Federation** dialog appears. Copy the entire example code block to a local text file using the copy button.
 
     <img
       src="./images/quickstart/publish-your-schema.jpg"
@@ -472,7 +472,7 @@ In this step, you'll create an empty supergraph in GraphOS Studio and then publi
 
     </Caution>
 
-4. Leave the dialog open; you'll complete setup with Rover.
+5. Leave the dialog open; you'll complete setup with Rover.
 
 #### Publish subgraph schemas