Docs: Versioning considerations

[AdrianoKF]

A few observations on the use of docs versions:

• latest (a pre-release version) is set as the default docs version. This causes the notification banner to be shown - however, the link in the banner links to the default version (i.e., by clicking on it, you are still looking at the pre-release docs).
• There is only one stable version. Going forward, this might confuse users, who cannot access the docs for previous stable releases.

I propose adopting the same versioning scheme as for lakeFS-spec, with latest as an alias for the latest stable version and set as the default. Pre-releases are labeled as development in that scheme.