Official rocky linux support

Hi,

RedHat deprecated Centos 8 and created Centos 8 Stream. Pi-hole followed the transition and now supports Centos 8 Stream instead of Centos 8 (Switch from centos8 to centos8:stream base image for centos 8 tests · pi-hole/pi-hole@444526a · GitHub).

Despite these changes, I would say that a considerable amount of users didn't change to Centos 8 Stream but rather other projects, like Rocky Linux and Alma Linux, that mimic the original goal of the Centos project.

I've been using Rocky Linux 8 for 6 months with pihole, without any problem. If you search for Rocky Linux in this forum, you'll find other people using it. Additionally, there is also an issue on Github asking for official support (Rocky Linux not supported, but workks · Issue #4604 · pi-hole/pi-hole · GitHub).

I think it would be nice to support officially Rocky Linux 8. This doesn't require changes in the code since, in the past, pihole supported Centos 8.

I'm supporting this, I've been using Pi-hole under Rocky for at least 6 months.