Change CHANGELOG.md references from pull requests to authors (#9864)

Add `rake repo:changelog` to do that automatically

lib/tasks/repo.rake

 # frozen_string_literal: true
 
 namespace :repo do
-  desc 'Generate the authors.md file'
+  desc 'Generate the AUTHORS.md file'
   task :authors do
-    file = File.open('AUTHORS.md', 'w')
+    file = File.open(Rails.root.join('AUTHORS.md'), 'w')
     file << <<~HEADER
       Mastodon is available on [GitHub](https://github.com/tootsuite/mastodon)
       and provided thanks to the work of the following contributors:
@@ -27,4 +27,50 @@ namespace :repo do
       This document is provided for informational purposes only. Since it is only updated once per release, the version you are looking at may be currently out of date. To see the full list of contributors, consider looking at the [git history](https://github.com/tootsuite/mastodon/graphs/contributors) instead.
     FOOTER
   end
+
+  desc 'Replace pull requests with authors in the CHANGELOG.md file'
+  task :changelog do
+    path = Rails.root.join('CHANGELOG.md')
+    tmp  = Tempfile.new
+
+    HttpLog.config.compact_log = true
+
+    begin
+      File.open(path, 'r') do |file|
+        file.each_line do |line|
+          if line.start_with?('-')
+            new_line = line.gsub(/#([[:digit:]]+)*/) do |pull_request_reference|
+              pull_request_number = pull_request_reference[1..-1]
+              response = nil
+
+              loop do
+                response = HTTP.headers('Authorization' => "token #{ENV['GITHUB_API_TOKEN']}").get("https://api.github.com/repos/tootsuite/mastodon/pulls/#{pull_request_number}")
+
+                if response.code == 403
+                  sleep_for = (response.headers['X-RateLimit-Reset'].to_i - Time.now.to_i).abs
+                  puts "Sleeping for #{sleep_for} seconds to get over rate limit"
+                  sleep sleep_for
+                else
+                  break
+                end
+              end
+
+              pull_request = Oj.load(response.to_s)
+              "[#{pull_request['user']['login']}](#{pull_request['html_url']})"
+            end
+
+            tmp.puts new_line
+          else
+            tmp.puts line
+          end
+        end
+      end
+
+      tmp.close
+      FileUtils.mv(tmp.path, path)
+    ensure
+      tmp.close
+      tmp.unlink
+    end
+  end
 end