code-server: add preserve host header instruction (#1645)

Author: calebdoxsey

content/docs/guides/code-server.mdx

@@ -82,6 +82,7 @@ In the Zero Console:
 5. In `To:`, add the internal URL
 6. In the **Policies** field, select the Codeserver policy
 7. Select the **Timeouts** tab and **Allow Websockets**
+8. Select the **Headers** tab and **Preserve Host Header**
 
 ## Add Docker Compose Services