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/services/contacts/contactable_inboxes_service.rb

@@ -0,0 +1,52 @@
+class Contacts::ContactableInboxesService
+  pattr_initialize [:contact!]
+
+  def get
+    account = contact.account
+    account.inboxes.map { |inbox| get_contactable_inbox(inbox) }.compact
+  end
+
+  private
+
+  def get_contactable_inbox(inbox)
+    return twilio_contactable_inbox(inbox) if inbox.channel_type == 'Channel::TwilioSms'
+    return email_contactable_inbox(inbox) if inbox.channel_type == 'Channel::Email'
+    return api_contactable_inbox(inbox) if inbox.channel_type == 'Channel::Api'
+    return website_contactable_inbox(inbox) if inbox.channel_type == 'Channel::WebWidget'
+
+    nil
+  end
+
+  def website_contactable_inbox(inbox)
+    latest_contact_inbox = inbox.contact_inboxes.where(contact: @contact).last
+    return unless latest_contact_inbox
+    # FIXME : change this when multiple conversations comes in
+    return if latest_contact_inbox.conversations.present?
+
+    { source_id: latest_contact_inbox.source_id, inbox: inbox }
+  end
+
+  def api_contactable_inbox(inbox)
+    latest_contact_inbox = inbox.contact_inboxes.where(contact: @contact).last
+    source_id = latest_contact_inbox&.source_id || SecureRandom.uuid
+
+    { source_id: source_id, inbox: inbox }
+  end
+
+  def email_contactable_inbox(inbox)
+    return unless @contact.email
+
+    { source_id: @contact.email, inbox: inbox }
+  end
+
+  def twilio_contactable_inbox(inbox)
+    return unless @contact.phone_number
+
+    case inbox.channel.medium
+    when 'sms'
+      { source_id: @contact.phone_number, inbox: inbox }
+    when 'whatsapp'
+      { source_id: "whatsapp:#{@contact.phone_number}", inbox: inbox }
+    end
+  end
+end