Backport Versions menu to 15.1
This MR adds the new Versions menu to the 15.2 docs site.
This was released and then rolled back, so this MR:
- Reverts this revert: !2931 (merged)
- Adds this fix: !2936 (merged)
How to test
See !2970 (merged).
These are the same changes and can be tested with the same steps, just use 15.1
anywhere 15.2
is referenced.