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>

spec/enterprise/models/account_spec.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Account do
+  describe 'usage_limits' do
+    before do
+      create(:installation_config, name: 'ACCOUNT_AGENTS_LIMIT', value: 20)
+    end
+
+    let!(:account) { create(:account) }
+
+    it 'returns max limits from global config when enterprise version' do
+      expect(account.usage_limits).to eq(
+        {
+          agents: 20,
+          inboxes: ChatwootApp.max_limit
+        }
+      )
+    end
+
+    it 'returns max limits from account when enterprise version' do
+      account.update(limits: { agents: 10 })
+      expect(account.usage_limits).to eq(
+        {
+          agents: 10,
+          inboxes: ChatwootApp.max_limit
+        }
+      )
+    end
+  end
+end