build.kde.org migration to Gitlab CI

Tracker task for planning of the build.kde.org migration to the Gitlab CI. Currently not much detail, but I will fill-in more details and to-do items in this list as we go.

Changes in docker images
Work on CI templates for the Gitlab CI: https://invent.kde.org/sysadmin/ci-tooling/-/tree/master/invent can serve as a starting point
Enable CI templates for the various components in phases
Figure out how to effectively do the dependency builds
Once all builds are migrated, shutdown and archive the build.kde.org jenkins instance

Edited Oct 25, 2022 by Ben Cooksley

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information