feat: Business hours

Data models and APIs for business hours

ref: #234

app/models/inbox.rb

@@ -11,6 +11,8 @@
 #  greeting_enabled       :boolean          default(FALSE)
 #  greeting_message       :string
 #  name                   :string           not null
+#  out_of_office_message  :string
+#  working_hours_enabled  :boolean          default(FALSE)
 #  created_at             :datetime         not null
 #  updated_at             :datetime         not null
 #  account_id             :integer          not null
@@ -24,6 +26,7 @@
 class Inbox < ApplicationRecord
   include Reportable
   include Avatarable
+  include OutOfOffisable
 
   validates :account_id, presence: true