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

app/controllers/concerns/request_exception_handler.rb

@@ -31,6 +31,10 @@ module RequestExceptionHandler
     render json: { error: message }, status: :unprocessable_entity
   end
 
+  def render_payment_required(message)
+    render json: { error: message }, status: :payment_required
+  end
+
   def render_internal_server_error(message)
     render json: { error: message }, status: :internal_server_error
   end

app/models/account.rb

@@ -6,6 +6,7 @@
 #  auto_resolve_duration :integer
 #  domain                :string(100)
 #  feature_flags         :integer          default(0), not null
+#  limits                :jsonb
 #  locale                :integer          default("en")
 #  name                  :string           not null
 #  settings_flags        :integer          default(0), not null
@@ -19,6 +20,7 @@ class Account < ApplicationRecord
   include FlagShihTzu
   include Reportable
   include Featurable
+  prepend_mod_with('Account')
 
   DEFAULT_QUERY_SETTING = {
     flag_query_mode: :bit_operator,
@@ -107,6 +109,13 @@ class Account < ApplicationRecord
     super || GlobalConfig.get('MAILER_SUPPORT_EMAIL')['MAILER_SUPPORT_EMAIL'] || ENV.fetch('MAILER_SENDER_EMAIL', 'Chatwoot <accounts@chatwoot.com>')
   end
 
+  def usage_limits
+    {
+      agents: ChatwootApp.max_limit,
+      inboxes: ChatwootApp.max_limit
+    }
+  end
+
   private
 
   def notify_creation