CI: Auto-create a release draft in the release workflow?

[leofang]

Currently we assume that a draft is created prior to running the release workflow:

cuda-python/.github/workflows/release.yml

Line 7 in ee6b92e

description: Manually-triggered release workflow. Must have a release note in the draft state and the release commit tagged.

I dunno how @vzhurba01 @rwgk feel about this, but perhaps the UX could be improved if we create the draft as part of the release workflow using gh release create --draft. After the wheels and docs are deployed and tarball/checksum attached to the draft, we then manually populate the release message in the draft and publish it.