ci: rebrand nightly releases as preview releases

[ematipico]

Summary

This PR does the following:

• creates a new workflow called preview.yml which we can use to create Preview releases. Preview releases are the "new nightlies", where a preview release is only built upon a workflow dispatch and approval of a core contributors. While nightly releases are good, they use a lot of compute time in the CI and don't publish all of them.
• it moves the shared logic for building the binaries inside a composite job, so we don't repeat ourselves
• preview releases and prod releases will have two separate workflows/files

This new preview workflow relies on the the changeset snapshot release. They have their own naming convention, but I believe it's fine.

Test Plan

Proof read. I will test it once we will merge next to main