Storage for Qt Ultralight CI build caching

In order to store cached results when building in CI, I need some storage space.

• It should be fast to access from COIN and and gitlab runners.
• Developers should be able to access it too, but no speed requirements here
• Files and folders have to be able to be created, written, uploaded, deleted and read
• Getting file/folder listings would be nice but is optional
• The last access time for files should be tracked and provided to allow to wipe unused files regularly