Avoid getByEmail calls when sending Orders and Carts to Mailchimp

[ihor-sviziev]

Issue Description

Preconditions

1. Magento CE 2.2.6 without sample data is installed.
2. mc-magento2 1.0.30.
3. ~100k orders that we want to sync to Mailchimp

Steps to reproduce

N/A

Actual and Expected result

Right now cron job ebizmart_ecommerce runs every 5 minutes and took ~4 minutes for me. Preparing orders info takes ~3.5 minutes of that time

Additional information

During preparing orders export there is two calls to Mailchimp API for getting customer info:

1. mc-magento2/Model/Api/Order.php

   Line 369 in 0c5d379

   $customers = $api->ecommerce->customers->getByEmail($mailchimpStoreId, $order->getCustomerEmail());

2. mc-magento2/Model/Api/Order.php

   Line 391 in 0c5d379

   $customer = $api->ecommerce->customers->get($mailchimpStoreId, $order->getCustomerId(), 'email_address');

As result of 2nd requests we usually getting following error in logs:

[2018-11-09 12:14:05] MailChimpLogger.INFO: Resource Not Found for Api Call: [https://us11.api.mailchimp.com/3.0/ecommerce/stores/c165314426294f1f4aff49977407e962/customers/353087?fields=email_address] using method [GET]
	Detail: [The requested resource could not be found.]
	Params:
		{"fields":"email_address"}
 [] []

Usually these requests took ~0.2 seconds each.

How it can be improved:

1. Create table with following info - mailchimp store id, mailchimp customer id and email.
2. During customers export - export customers that are needed for orders at first, then fill up this table
3. When exporting customers - export customers that required for orders sync at first
4. during orders export - use data from table for getting this info.

[gonzaloebiz]

Hi @ihor-sviziev

thanks for your feedback.
We are open to PR

Best