Add support for multiple MailChimp accounts

I did a brief search but did not find any existing requests for handling multiple MailChimp accounts.

Problem/Motivation

I have a use case in which I need to add multiple MailChimp accounts to be used on one Drupal site. I have group A that needs to manage List A, and group B that needs to manage List B, but group B should not have access to List A.

Right now in this scenario, the lists have to be in separate MailChimp accounts. This is because within a MailChimp account, there is no way to restrict access to manage only a specific list (or segment), the existing access levels are account-wide. You either get access to all the lists, or none.

Proposed resolution

Allow adding multiple MailChimp accounts/keys. This would permit group B to have a subscription form that populates List B, and group A to have a subscription form for List A.

Remaining tasks

User interface changes

API changes

Data model changes