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>

app/controllers/api/v1/accounts/agents_controller.rb

@@ -2,6 +2,7 @@ class Api::V1::Accounts::AgentsController < Api::V1::Accounts::BaseController
   before_action :fetch_agent, except: [:create, :index]
   before_action :check_authorization
   before_action :find_user, only: [:create]
+  before_action :validate_limit, only: [:create]
   before_action :create_user, only: [:create]
   before_action :save_account_user, only: [:create]
 
@@ -69,4 +70,8 @@ class Api::V1::Accounts::AgentsController < Api::V1::Accounts::BaseController
   def agents
     @agents ||= Current.account.users.order_by_full_name.includes({ avatar_attachment: [:blob] })
   end
+
+  def validate_limit
+    render_payment_required('Account limit exceeded. Upgrade to a higher plan') if agents.count >= Current.account.usage_limits[:agents]
+  end
 end