Add v5 to sidebar (#6504)

* Add v5 to sidebar

* Add banner

* Fix labels

* Link banner to current docset homepage

* Fix hrefs

Author: Meschreiber

docs/source/_sidebar.yaml

@@ -1,13 +1,20 @@
+banner:
+  message: "You are viewing documentation for a preview version of this software."
+  link:
+    href: "./#previews"
+    content: "Learn about previews."
 switcher:
   heading: "Apollo Kotlin"
   versions:
+    - label: v5
+      href: ./
     - label: v4
       latest: true
-      href: ./
+      href: ../v4
     - label: v3
-      href: ./v3
+      href: ../v3
     - label: v2
-      href: ./v2
+      href: ../v2
 items:
   - label: Get Started
     href: "."