Add Merge Tags feature to plugin

[oth]

It would be great if the Mailchimp plugin had the Merge Tag feature. Then nopCommerce store owners would be able to assign them to the default values between nopCommerce and Mailchimp

Merge Tags <--> nopCommerce
FNAME = First Name (already syncing)
LNAME = Last Name (already syncing)
ADDRESS = Address (already syncing)

PHONE = Phone number
BIRTHDAY = Birthday

It would help with campaigns and having better information about the customer

See: https://mailchimp.com/help/all-the-merge-tags-cheat-sheet/#Personalization

Even better would be for the plugin to get available Merge Tags from the Mailchimp account and make it possible for the admin to customize what fields within nopCommerce should equal a specific merge tag from Mailchimp