Added gem for generating the change log file.

.github_changelog_generator

@@ -0,0 +1,8 @@
+user=zammad
+project=zammad
+output=CHANGELOG.md
+since-tag=1.0.0
+bug-labels=bug,minor bug,security
+enhancement-labels=enhancement,feature
+issue-line-labels=enhancement,feature,bug,minor bug,security
+exclude-tags=9.0.1,0.9.1,v0.1.8,v0.1.7,unittests_passed

Gemfile

@@ -105,6 +105,9 @@ group :development, :test do
   gem 'pre-commit'
   gem 'rubocop'
   gem 'coffeelint'
+
+  # changelog generation
+  gem 'github_changelog_generator'
 end
 
 gem 'puma'