Extend documentation about community products

After we finish the work described in [building custom products milestone](https://github.com/AlmaLinux/build-system/milestone/1), we need to ensure that:
* [this wiki page](https://github.com/AlmaLinux/build-system/wiki/ALBS:-Guide-for-Authorised-Users#community-repositories) is extended/updated accordingly to reflect the last changes around community products
* If needed, create a dedicated wiki page describing the workflow of community products