Docs sidebar styling is different for latest vs stable

[ejm714]

latest

stable

The latest one is correct so we need to get stable to use the same.

While we're making this change, let's also:

• [ ] make Changelog a clickable header or set a non-header page for Contribute to zamba. Right now we have two different behaviors for single page sections

It may be the case that the previous version configuration is not set up correctly, as "v2" is not using what's on master currently. Eg. the homepage is different, the changelog page still has "TODO" text for the date

• [ ] Update stable v2 configuration

[ejm714]

Fixed by release workflow run as part of https://github.com/drivendataorg/zamba/pull/161