[#139] Send conversation emails (#442)

* [#139] Delayed emails for conversations

* Added the setex and get methods to Redis wrapper
* Set the priorities for the sidekiq queues
* Was not able to use mailhog for testing email in local, switched back to letter opener and added comments on using the SMTP settings
* Added after create hood in messages to queue the sending of mail after 2 minutes using sidekiq worker and also set the redis key for the conversation to avoid the email sending for every message
* Added the sidekiq worker to send the email and delete the conversation redis key
* Added the mailer and mail template
* mailer sends the last 10 messages along with the new messages from the time it was queued

* Send email only in development or if smtp config is set

* Send email only in development or if smtp config is set
* Set the SMTP_PORT in production variable

* Adding redis to circle CI

* Specs for the conversation email changes

* Added specs for conversation email sidekiq worker
* Added specs for conversation mailer
* Added specs in message model for the after create hook for notify email

* Send emails only when there is a reply from agent

* set development to use mailhog

* Adding comments for using letter opener

spec/models/message_spec.rb

@@ -22,5 +22,11 @@ RSpec.describe Message, type: :model do
       expect(::MessageTemplates::HookExecutionService).to have_received(:new).with(message: message)
       expect(hook_execution_service).to have_received(:perform)
     end
+
+    it 'calls notify email method on after save' do
+      allow(message).to receive(:notify_via_mail).and_return(true)
+      message.save!
+      expect(message).to have_received(:notify_via_mail)
+    end
   end
 end