Add support for `latest` in the `UpdateReleaseBuilder`

As part of the GitHub API, there is a make_latest field that allows marking an existing as Latest. I think this would be useful for the builder to support

octocrab/src/api/repos/releases.rs

Line 389 in 7e280be

    
           pub struct UpdateReleaseBuilder<'octo, 'repos, 'handler, 'tag_name, 'target_commitish, 'name, 'body>

Let me know if you have concerns, I would be happy to open a PR.

Thank you for your issue! Feel free to make a PR adding it 🙂