feat: SLA CRUD APIs (EE) (#7027)

Fixes: https://linear.app/chatwoot/issue/CW-1613/sla-api

Co-authored-by: Sojan Jose <sojan@pepalo.com>

enterprise/app/models/enterprise/enterprise_account_concern.rb

@@ -0,0 +1,7 @@
+module Enterprise::EnterpriseAccountConcern
+  extend ActiveSupport::Concern
+
+  included do
+    has_many :sla_policies, dependent: :destroy_async
+  end
+end

enterprise/app/models/sla_policy.rb

@@ -0,0 +1,21 @@
+# == Schema Information
+#
+# Table name: sla_policies
+#
+#  id                         :bigint           not null, primary key
+#  frt_threshold              :float
+#  name                       :string           not null
+#  only_during_business_hours :boolean          default(FALSE)
+#  rt_threshold               :float
+#  created_at                 :datetime         not null
+#  updated_at                 :datetime         not null
+#  account_id                 :bigint           not null
+#
+# Indexes
+#
+#  index_sla_policies_on_account_id  (account_id)
+#
+class SlaPolicy < ApplicationRecord
+  belongs_to :account
+  validates :name, presence: true
+end