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>

db/migrate/20211012135050_add_limits_to_accounts.rb

@@ -0,0 +1,5 @@
+class AddLimitsToAccounts < ActiveRecord::Migration[6.1]
+  def change
+    add_column :accounts, :limits, :jsonb, default: {}
+  end
+end

db/schema.rb

@@ -52,6 +52,7 @@ ActiveRecord::Schema.define(version: 2021_12_08_085931) do
     t.integer "settings_flags", default: 0, null: false
     t.integer "feature_flags", default: 0, null: false
     t.integer "auto_resolve_duration"
+    t.jsonb "limits", default: {}
   end
 
   create_table "action_mailbox_inbound_emails", force: :cascade do |t|