fix(metrics): ensure email sent amplitude events include device id

[philbooth]

Related to mozilla/fxa-activity-metrics#109.

Currently our fxa_email - sent amplitude events do not include the device id, which may be causing problems with the funnels with Amplitude. This change fixes it by passing the device id to the mailer in our sign-in, sign-up and reset flows, and also by setting the property on the correct object when calling the amplitude module.

Here is an example event from before these changes (without device_id):

{"op":"amplitudeEvent","event_type":"fxa_email - sent","time":1543488875186,"user_id":"92edc9c2522745d29c96d99daab0f759","session_id":1543488852908,"app_version":"126","language":"en","event_properties":{"email_type":"reset_password","email_provider":"other","email_sender":"ses","email_service":"fxa-auth-server","email_template":"recoveryEmail","email_version":1},"user_properties":{"flow_id":"ddb4d3455676fc74125b0e90f744b9563c9f855a1501f270028a01d6721e30c7","sync_device_count":0,"sync_active_devices_day":0,"sync_active_devices_week":0,"sync_active_devices_month":0}}

And here is an example event after these changes (with device_id):

{"op":"amplitudeEvent","event_type":"fxa_email - sent","time":1543495408243,"user_id":"0bc26f36d7044a6a94e115eced630b2e","device_id":"593cb512c5284c298bb1c8a9b3c03dd9","session_id":1543495397648,"app_version":"126","language":"en","event_properties":{"email_type":"reset_password","email_provider":"other","email_sender":"ses","email_service":"fxa-auth-server","email_template":"recoveryEmail","email_version":1},"user_properties":{"flow_id":"b03ec6df0e4318eb789038d2d1fa6781b913575168bece58039067e6dfe8f728","sync_device_count":0,"sync_active_devices_day":0,"sync_active_devices_week":0,"sync_active_devices_month":0}}

Opened against train-126 for a patch release as it's affecting metrics.

@mozilla/fxa-devs r?

[vbudhram]

@philbooth I see device_id in sign-in/sign-up/reset password amplitude events 👍🏽