Add release:create_github_release task

Leverages the `gh` CLI to create a release. This uses the same command that we specified in the README for releasing, but programmatically determines the version to specify and automatically crafts the proper release notes (linking to the CHANGELOG and the diff view).

tasks/release.rake

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
+require "date"
 require "rake"
+require "twirp/protoc_plugin/core_ext/string/to_anchor"
 
 desc "Gets the latest GitHub release version, e.g: v1.1.1"
 task "release:latest_github_release" do
@@ -9,3 +11,38 @@ task "release:latest_github_release" do
   # but we go through the `gh` because we want the latest _GitHub_ release.
   $stdout << `gh release view --json tagName --jq '.tagName'`
 end
+
+desc "Creates a GitHub release for v#{Bundler::GemHelper.gemspec.version}"
+task "release:create_github_release" do
+  github_release = `bundle exec rake release:latest_github_release`.chomp
+  version = Bundler::GemHelper.gemspec.version.to_s
+
+  notes = <<~NOTES
+    See [CHANGELOG.md](#{changelog_link(version)}) for release details.                                                                                                    
+                                                                                                                    
+    Full changes: #{compare_link(github_release, version)}
+  NOTES
+
+  `gh release create v#{version} --verify-tag --latest --notes "#{notes}"`
+end
+
+def repo_base_url
+  "https://github.com/collectiveidea/protoc-gen-twirp_ruby"
+end
+
+def changelog_link(version)
+  "#{repo_base_url}/blob/main/CHANGELOG.md##{changelog_heading(version).to_anchor}"
+end
+
+# @param version [String] the version, e.g. "1.2.0"
+def changelog_heading(version)
+  # Assume the heading in the CHANGELOG.md is always a consistent
+  # format: "[1.1.1] - 2024-05-22"
+  "[#{version}] - #{DateTime.now.strftime("%Y-%m-%d")}"
+end
+
+# @param previous_tag [String] the previous version tag, e.g. "v1.1.1"
+# @param current_version [String] the current version, e.g. "1.2.0"
+def compare_link(previous_tag, current_version)
+  "#{repo_base_url}/compare/#{previous_tag}...v#{current_version}"
+end