feat: disable tracking in transactional email

[KishenKumarrrrr]

Problem

AWS SES includes a 1x1 tracking pixel to detect whether or not a user has opened/read an email. GSIBs block this tracking pixel which causes it to appear as a little red X at the bottom of emails. This makes the emails appear suspicious.

In this PR, I add a feature to enable transactional email users to turn off this tracking feature via a new disable_tracking flag. This would prevent this issue from popping up.

Solution

The events that are tracked by SES is determined by the configuration set that SES uses when sending out the email. This configuration set is determined by the value of the X-SES-CONFIGURATION-SET header. Configuration sets are defined via the AWS console.

I've added an additional configuration set (postman-email-no-tracking) to ap-southeast-2 that does not include tracking Open and Read states. This prevents the gif from being added.

Additionally, the transactional email request body now includes an optional disable_tracking field that users can set to true if they don't want the tracking pixel to be added. When tracking is disabled, we will use the postman-email-no-tracking configuration set instead of the default postman-email-open configuration set.

Deployment Notes

New Env Vars

• BACKEND_SES_NO_TRACKING_CONFIGURATION_SET : Name of SES configuration set that does not include tracking open/read events