Allow customizing Github release title

It'd be nice if you could customize the format of the title of each generated Github release. Currently, it looks like it pulls the title from the changelog if available, and uses the format `x.y.z - yyyy-mm-dd`. If there's no changelog, it just uses the git tag. I'm not 100% sure on that though, just my observation.

I'd like to customize that so the title is always in the format `vx.y.z`. I read through `announce.rs` a bit and didn't see an obvious place where this could be done, but I could take a crack at it with some direction.

Start by reading announce.rs, which the issue identifies as related to release title generation, and trace how changelog titles, date-formatted titles, and git tags are selected. Done means generated GitHub release titles can be customized and support the requested vx.y.z format; verify the behavior using the repository's existing release-related checks, if present.

Written by the indexing model from the issue text.