Add gh release update

[kzu]

Describe the feature or problem you’d like to solve

Currently you can gh release create and gh release upload, but editing of the release notes themselves is not possible.

This would be very useful to automate changelog generation, for example, so that:

1. Human creates a release on GitHub Releases page, gives it the desired tag name
2. Workflow runs, generates a changelog, and updates the release notes with that using the GH CLI

Proposed solution

I see two choices here:

1. Introduce a new update command, likely with most (all?) arguments from create
2. Extend the upload and add -n, --notes and -F, --notes-file args and make files optional (not sure if it is already), so that upload can simply update the notes while (optionally) uploading files.

Additional context

I'm aware that this is almost trivially achieved with plain REST calls or pre-built GH actions in the marketplace. But I'm leaning towards simplifying workflows by having very explicit GH CLI calls instead, so it's very clear what's being done at each workflow step, and customizability is boundless.

[mislav]

Thank you for the feature request! Editing different aspects of a release comes up as a feature request from time, so I'm going to merge all existing issues as duplicate of #1997