Drop abandoned add-on (Sosivio)

Sosivio seems to be abandoned, there's no Github activity and the
website is down [1][2].

The helm registry is also down[3], which is currently blocking the
Microk8s CI.

That being considered, we'll drop the Sosovio add-on.

[1] https://github.com/Sosivio
[2] https://docs.sosiv.io/
[3] https://helm.sosiv.io/

Author: petrutlucian94