chore: Validation for purchased pricing_plan_quantity (#8809)

- Add validations based on purchased pricing_plan_quantity
- Modify the Dashboard to support the new error message

enterprise/app/models/enterprise/concerns/user.rb

@@ -0,0 +1,13 @@
+module Enterprise::Concerns::User
+  extend ActiveSupport::Concern
+
+  included do
+    before_validation :ensure_installation_pricing_plan_quantity
+  end
+
+  def ensure_installation_pricing_plan_quantity
+    return unless ChatwootHub.pricing_plan == 'premium'
+
+    errors.add(:base, 'User limit reached. Please purchase more licenses from super admin') if User.count >= ChatwootHub.pricing_plan_quantity
+  end
+end