When testing out these scripts on a fork, I realized that it was more
convenient to use a single environment variable (e.g.,
`GITHUB_API_URL=... ci/draft-release.sh`) to change some of the script's
input parameters.
Previously, the release process for wasi-sdk was undocumented and
manual. The `RELEASING.md` document in this commit describes the steps
necessary to publish a new version of `wasi-sdk` as a GitHub release and
provides helpful scripts to automate some of the steps.
With this in place, a future change could add a workflow trigger that
allows running the steps automatically in GitHub actions. Keeping the
steps as scripts in the repository, however, allows developers to re-run
steps themselves in the (likely) case that something goes awry.