Accept `issue new` as command to create an issue

Now only `/trigger issue create` is a valid command, but our UI shows
Issue new everywhere. The default now will be `/trigger issue new`. The
help message is adjusted to reflect this.

Fixes: gitlab-org/gitlab-ce#25025

changelogs/unreleased/zj-issue-new-over-issue-create.yml

+---
+title: Accept issue new as command to create an issue
+merge_request: 
+author: 

lib/gitlab/chat_commands/issue_create.rb

@@ -4,11 +4,11 @@ module Gitlab
       def self.match(text)
         # we can not match \n with the dot by passing the m modifier as than 
         # the title and description are not seperated
-        /\Aissue\s+create\s+(?<title>[^\n]*)\n*(?<description>(.|\n)*)/.match(text)
+        /\Aissue\s+(new|create)\s+(?<title>[^\n]*)\n*(?<description>(.|\n)*)/.match(text)
       end
 
       def self.help_message
-        'issue create <title>\n<description>'
+        'issue new <title>\n<description>'
       end
 
       def self.allowed?(project, user)

spec/lib/gitlab/chat_commands/issue_create_spec.rb

@@ -57,5 +57,12 @@ describe Gitlab::ChatCommands::IssueCreate, service: true do
       expect(match[:title]).to eq('my title')
       expect(match[:description]).to eq('description')
     end
+
+    it 'matches the alias new' do
+      match = described_class.match("issue new my title")
+
+      expect(match).not_to be_nil
+      expect(match[:title]).to eq('my title')
+    end
   end
 end