chore: Introduce enterprise edition license (#3209)

- Initialize an "enterprise" folder that is copyrighted.
- You can remove this folder and the system will continue functioning normally, in case you want a purely MIT licensed product.
- Enable limit on the number of user accounts in enterprise code.
- Use enterprise edition injector methods (inspired from Gitlab).
- SaaS software would run enterprise edition software always.

Co-authored-by: Pranav Raj S <pranav@chatwoot.com>

enterprise/app/models/enterprise/account.rb

@@ -0,0 +1,15 @@
+module Enterprise::Account
+  def usage_limits
+    {
+      agents: get_limits(:agents),
+      inboxes: get_limits(:inboxes)
+    }
+  end
+
+  private
+
+  def get_limits(limit_name)
+    config_name = "ACCOUNT_#{limit_name.to_s.upcase}_LIMIT"
+    self[:limits][limit_name.to_s] || GlobalConfig.get(config_name)[config_name] || ChatwootApp.max_limit
+  end
+end