[DX Streamline] Create draft GitHub releases on PRs modifying version.go

[galargh]

Problem to solve

Right now, a GitHub Release is created only after a PR modifying version.go is merged. This makes it impossible to verify the release or update its description prior to the merge. It also means that the release, on publish, is not yet ready for general public fully (lacking proper description).

Why Important

As soon as a really is out, it should be final - including the description part. By creating drafts on PRs, we'll be able to prepare all the aspects of the release prior to merge.

User/Customer

Lotus maintainers

Notes

Enabled by #12096

[galargh]

When working on this, we should ensure that the replace_existing_draft setting of the goreleaser works as expected. Ideally, we want to be able to create a draft on a PR, be able to update it, and for those updates to survive any new pushes to the PR.