K8SSAND-1830 ⁃ Enable version selector to K8ssandra documentation

[mieslep]

Is your feature request related to a problem? Please describe.
When reading documentation, i.e. at https://docs-v2.k8ssandra.io/, what shows is naturally the most recent version. However, it is possible (and likely?) that users will want to review documentation for an older version. For example, v1.3 might be the latest, but the documentation for that version may not work when applied to v1.2.

Describe the solution you'd like
In the Cassandra documentation, https://cassandra.apache.org/doc/latest/ , there is a drop-down that allows one to view a specific version of the documentation. A selector similar to that would be useful.

Describe alternatives you've considered
One needs to look at raw documentation via the release tag...not so optimal!

┆Issue is synchronized with this Jira Task by Unito
┆friendlyId: K8SSAND-1830
┆priority: Medium

[mieslep]

@jsanda here you go!