Implement github-changelog-generator to generate CHANGELOG.md

In the Vox Pupuli tradition, use labels in GitHub issues to generate a
human readable changelog when we release a new version of the code.

Author: smortex

Gemfile

@@ -66,6 +66,7 @@ group(:development, optional: true) do
 end
 
 group(:packaging) do
+  gem 'github_changelog_generator'
   gem 'packaging', *location_for(ENV['PACKAGING_LOCATION'] || '~> 0.99')
 end
 

Rakefile

@@ -131,3 +131,30 @@ if Rake.application.top_level_tasks.grep(/^gettext:/).any?
     abort("Run `bundle install --with documentation` to install the `gettext-setup` gem.")
   end
 end
+
+begin
+  require "github_changelog_generator/task"
+  require_relative "lib/puppet/version"
+
+  GitHubChangelogGenerator::RakeTask.new :changelog do |config|
+    config.header = <<~HEADER.chomp
+    # Changelog
+
+    All notable changes to this project will be documented in this file.
+    HEADER
+    config.user = "openvoxproject"
+    config.project = "puppet"
+    config.exclude_labels = %w[dependencies duplicate question invalid wontfix wont-fix modulesync skip-changelog]
+    config.since_tag = "7.36.1"
+    config.future_release = Puppet::PUPPETVERSION
+    # FIXME: The following should be enough to ignore versions in the main
+    # branch only, but this does not work.  For now we rely on a regexp to
+    # exclude tags that should not be matched.
+    config.release_branch = "7.x"
+    config.exclude_tags_regex = /\A8\./
+  end
+rescue LoadError
+  task :changelog do
+    abort("Run `bundle install --with packaging` to install the `github_changelog_generator` gem.")
+  end
+end