Automatic release notification in SpiceDB and zed

The Authzed team has implemented a project to make it transparent to end-users when new versions of SpiceDB are available for update. This is achieved by adding a check in SpiceDB and zed, which uses the GitHub API to determine if there's a newer version available, and logs an error message to the user with the latest released version if the current version is outdated. The project also adds middleware to both SpiceDB and zed to report the server's current version in gRPC response headers, allowing users to check for updates directly from within their applications.