Allow linking to the latest documentation with the specific version

This is more of a "hosting the documentation" kind of issue, and might not be the right place for it. But thought to report it here anyway, since it seems to affect just Barman cloud plugin and I couldn't figure out a better place for it.

Currently it isn't possible to link to the latest plugin version documentation with a version specific link. I.e.
- works
- does not work
- works

This means that when writing documentation like "here's the list of relevant documentation on different software we're using", one can't link to the correct version. Which leads to documentation like "remember to double check that the documentation version matches the version on the list!".

No file, test, or entry point is named. Start by reproducing the working and failing documentation URLs and locating the hosting configuration for versioned Barman Cloud plugin docs. Done means the latest plugin version, including 0.9.0, is reachable through a version-specific documentation link.

Written by the indexing model from the issue text.