Snapshot Publishing

[nodh]

          So apparently, the jvmTest action [disables composite builds](https://github.com/a-sit-plus/vck/actions/runs/10881884620/workflow#L16). I've now reverted this change, BUT we need to have a strategy for testing releases. My proposal: Introduce an `allTests` action that disables composite builds, which will run only on `release/xxx` branches an `main`. D'Accord?!

FYI: snapshot publishing works now for Signum, so we can depend on the actual version catalogs of the signum commit included in the composite build. We should, however, pin this snapshot version to a specific build (e.g. 4.0.0-20240917.201628-3 for indispensable and 0.3.0-20240917.201628-6 for Supreme. if you agree, just assign me an issue with reference to this comment.

Originally posted by @JesusMcCloud in #125 (comment)