Change AltImage documentation to use gitlab.com repo
# CentOS Infra issue/request
## Issue Type
* [] Issue - problem with something that was working
* [x] Feature Request - something you'd like us to add/modify/change
* [] Task - mostly used by CentOS Infra team for day-to-day operations or bigger plans
## Description
Alternative Images SIG has moved everything from pagure.io to gitlab.com
Please do whatever is needed to change our documentation to now point to our gitlab area at https://gitlab.com/CentOS/AltImages/sig/-/tree/main/docs
issue