Add rake changelog

Author: sue445

Rakefile

@@ -14,6 +14,15 @@ task :release do
   end
 end
 
+desc "Generate changelog entry"
+task :changelog, [:before, :after] do |_, params|
+  args = []
+  args << "--before #{params.before}" if params.before
+  args << "--after #{params.after}" if params.after
+
+  sh "ruby _tools/changelog_generator/changelog_generator.rb #{args.join(" ")}"
+end
+
 task build_all: %w[ruby:build_all go:build_all go_gem:test ruby_h_to_go:test patch_for_go_gem:test]
 
 task default: :build_all