feat: Contactable Inboxes API (#2101)

- Add endpoint which lists inboxes through which a contact can be contacted
- Conversation creation API auto-creates contact_inbox for specific channels [ Twilio, email, api]
- Ability to send the initial message payload along with the conversation creation
- Fixes #1678 ( issue saving additional attributes for conversation )

app/controllers/api/v1/accounts/contacts_controller.rb

@@ -4,7 +4,7 @@ class Api::V1::Accounts::ContactsController < Api::V1::Accounts::BaseController
 
   before_action :check_authorization
   before_action :set_current_page, only: [:index, :active, :search]
-  before_action :fetch_contact, only: [:show, :update]
+  before_action :fetch_contact, only: [:show, :update, :contactable_inboxes]
 
   def index
     @contacts_count = resolved_contacts.count
@@ -40,6 +40,10 @@ class Api::V1::Accounts::ContactsController < Api::V1::Accounts::BaseController
 
   def show; end
 
+  def contactable_inboxes
+    @contactable_inboxes = Contacts::ContactableInboxesService.new(contact: @contact).get
+  end
+
   def create
     ActiveRecord::Base.transaction do
       @contact = Current.account.contacts.new(contact_params)